Joshua and Margaret are Jake's parents who first appeared in a flashback in "Memories of Boom Boom Mountain." Finn and Jake's parents are presumed dead, although when or how they died has not been revealed. During his flashback as a child in the episode "Crystals Have Power," Jake was shown to have a living brother named Jermaine. He has not been seen in-person; only in flashbacks and holograms. Jake is often reminded of his family, as shown in "Beautopia." In "Conquest of Cuteness," Jake tells Finn that sometimes he sounds like his mother. Despite Jake's relationship with his mother he is not her actual son as revealed in "Joshua and Margaret Investigations" where Joshua was poisoned by the Shape-shifter creating Jake. This makes the Shape-shifter Jake's biological "mother" and Margaret his adoptive/step-mother. However Joshua and Margaret never told Jake about this so he is unaware. In the episode, "Jermaine", it is revealed that Jake's half-brother, Jermaine, had been living in his family's house to protect his father's items that were taken from demons who wanted the items back. Upon Jake's return to the house, Jermaine cracks and yells at Jake, upset and jealous that Jake had always been Joshua's favorite and left Jermaine to deal with his father's mess while Jake went on to have adventures. By the end of the episode, the two settle the dispute and make up.
Finn and Jake are best friends and adoptive brothers. They will go out of their way to protect each other. Jake watches over Finn using his Stretchy Powers to protect him, whether it is shielding him from rain or cold weather, or catching him in mid-fall. Jake was fully aware of Finn's crush on Princess Bubblegum. He was also very supportive when he was heartsick from her and fully understands how much Princess Bubblegum had hurt him.
Having been raised together by Jake's parents, the two share a brotherly companionship. Jake often acts as a force of guidance in Finn's life, giving out advice or simply cheering him up in his own misguided ways. In "Incendium," he finds Finn a girlfriend in order for him to cope from Princess Bubblegum, and in "Burning Low," Jake gave Finn advice about his love life which shows Jake is doing his best to make sure Finn's relationship with Flame Princess does not turn out like his relationship with Princess Bubblegum. Though they have seemingly contrasting personalities, the pair make an excellent team and are immensely important figures in each other's lives.
It is known that Jake is not Finn's dog, but rather his friend and brother, while Finn sees himself as their son and fellow "puppy." Jake can sense when he is about to cry or feeling about to cry, he said that it is like a mother-daughter relationship. Sometimes, the two consider Jake as a real pet dog, like when Finn says "good dog" in "Rainy Day Daydream," or Jake catching a Frisbee similar to a traditional human-dog relationship in "Up a Tree."
However, there may be moments in which they could not settle their differences, like in "Video Makers," in which they ignore each other because of a dispute whether the movie should be an action adventure or a romantic comedy. In the episode "Who Would Win" after Finn destroys Jake's video game, Kompy's Kastle, Jake, in anger tells Finn that he's going to break every bone in his body and then heal his with the magic tears that Finn got from the Cyclops. However intense their fighting, it is noted that they always make up because of someone, whether it be BMO or the Dream Warrior.
Jake can be quite selfless when Finn is endangered and will willingly take physical punishment in order to shield his friend. In "James Baxter the Horse," Jake protected Finn from a punch that would have crushed them both, severely damaging his body in the process. The two have a fraternal bond and will stop at nothing to ensure each other's safety.In the episode "What Have You Done?", when Finn is seemingly hurt by the fact that Ice King could so easily drop his lifeless body, Jake consoles Finn by saying that if he came across Finn's lifeless body, he would clasp Finn dramatically for a 'kajillion' years.
In the episode "Shh!", when Finn and Jake compete to keep silent the whole day, only communicating with written signs, Finn was not able to carry out a normal conversation with the signs he had written. It is then revealed that most of Finn's signs were addressed to Jake and only Jake, including "Hi, Jake", "Thanks, Jake", "That's Funny, Jake", "Nice Catch, Jake", Go Get'm Jake!" and "You The Man, Jake!". Their close friendly and brotherly relationship is also displayed when Finn shows the sign "I Love You, Jake" when he was angry at Jake, and shows the sign "Jake Rules!" when he wanted to cheer Jake up.
In the episode "Dungeon Train", Jake shows genuine love and care for Finn, going as far as to promise to stay on the train with Finn, despite this being against Jake's wishes. Finn also shows his strong bond with Jake, when he was finally able to give up the convenient temptation of staying on the train forever, this willpower arguably fueled by his love for his brother, when he saw through the future crystal that Jake would have stayed on the train with him if he had continued the way he was. Jake was also shown to be truly happy when he found out Finn was going to be alright in the future.
Conversely, in the episode "Dentist" it is revealed from Tiffany that Jake had the skills and prowess to lead a successful life of crime as a 'Criminal Juggernaut', was it not for Finn's influence as Jake's younger brother and best friend, who tore Jake away from Tiffany and their life of crime. Similar to how Finn's love for Jake saved Finn from the Dungeon Train, it is also possible that Jake's love for Finn saved Jake from a life of crime. Furthermore in the same episode, Tiffany said that killing Finn would devastate Jake, a show of their strong bond as brothers and best friends.
In the episode "Ghost Fly", Jake was willing to let BMO momentarily kill him so that he could save Finn from the Ghost Fly's possession. At the end of the episode, when Jake's life was saved by defibrillation, Finn is seen to be extremely relieved and crying as well, demanding Jake to never leave him again.
Jake loves his children Charlie, T.V., Viola, Kim Kil Whan, and Jake Jr. deeply. When they were first born in "Jake the Dad," he was extremely excited to show them to Finn and BMO and became very emotional with his new family surrounding him. He even cried tears of joy when Finn told him how proud their mother would be of him. He even announced to Finn that he would be living with Lady and the pups from then on, which may conclude that Jake may love his puppies more than Finn.
Jake immediately became a watchful, attentive, and very over-protective father, constantly consulting his Mom's manual on how to raise and nurture the pups properly. Unfortunately, he took his job too seriously and, coupled with the paranoid advice from his mother's manual, he ended up wearing himself out over his children. He went as far as to watch them through binoculars until 4 a.m., perform CPR on them while they were sleeping (courtesy of his mother's advice), and leash them while they took a walk outside.
The pups on the other hand, who had inherited the trait of rapid aging from Lady, learned to take care of themselves in a short amount of time. When Jake was taken by a horde of foxes to be eaten, the pups banded together to create Super Pup, quickly defeating the enemies as Jake was too exhausted to defend himself.
Though Jake still cares for his children, he found himself moving back in with Finn, stating that, "The pups can pretty much take care of themselves. They don't really need me around... they're basically, like, older than me already."
In "Puhoy," Jake plays with BMO by tossing it up and down, which inspires BMO to ask why Jake does not do this with his actual children. Jake explains that Rainicorns age to adulthood in a few hours, which makes BMO ask if Jake regrets that. Jake becomes visibly sad before being distracted by Finn's return from the Pillow World.
Jake Jr. has been shown to look up to Jake, attempting to imitate his criminal past in "One Last Job." She is seen hanging out with Finn and Jake at the Tree Fort in "Another Five More Short Graybles," though Finn and Jake tend to treat her more like a small child than a (rapidly-aged) adult.
Jake expressed great pride upon finding out his son T.V. was still living with Lady and addicted to computer games in "Jake Suit." In this episode, he mentions that the other pups have all gotten apartments.
He also makes a short reference to them in "Dungeon Train" when he says "I wonder what my kids are doing." and then falls asleep. The five pups attended Tree Trunks' wedding to Mr. Pig with their parents in "Apple Wedding."
Jake's relationship with his puppies was shown to be more strained in "Ocarina," as their rapid aging has made them more emotionally mature than him. Jake Jr. and T.V. were both irate that they had not seen Jake in a while (T.V. notes, "I love Dad, but he's only ever met me twice"), while Kim Kil Whan takes on more of a disapproving father role toward Jake, trying to force him to get a job and grow up by buying the deed to the Tree Fort and becoming his landlord. By the end of the episode, though, Kim Kil Whan realizes his dad loves him and notes, "Dad's good." Viola, by contrast, makes excuses for Jake's absence in her life and expresses approval for all Jake's actions.
Jake spends a good amount of time with T.V. in the episode "The Diary," helping him track down the source of the teenage diary that turns out to belong to Nurse Pound Cake. He immediately grasps T.V.'s obsession with the diary, and seems to be trying to guide T.V. away from video games and being inside all the time, though he mostly lets his son make his own decisions. In "Flute Spell," he is shown taking T.V. to the Farmer's Market twice over a two-week period. It is unclear as to whether he knows T.V. has moved in with Lady Rainicorn's parents in the Crystal Dimension.
VIola spends some time with Jake in "Summer Showers." Jake repeatedly calls her "great" and indicates how proud he is that Viola is having success in her career as an actress, something that validates his insecure feelings about his success as a father. There are indications that Viola is somewhat insecure about living up to Jake's high opinion of her. On opening night of the play "Summer Showers," Jake brings the family to watch Viola's premiere, and uses his stretchy powers to create extra arms and fill the room with applause for Viola for her curtain call. Afterwards, when Viola admits to him she was originally just supposed to do the play's effects, Jake is even more proud of her for pulling double-duty. She and Jake repeatedly compliment each other as "amazing."
Charlie's personality appears to be closest to Jake's free-spirited nature, as seen in "Daddy-Daughter Card Wars." In the episode, Jake tricks Charlie into accompanying him to a Card Wars tournament based on her skills with Tarot cards, though Charlie is reluctant to participate in such a rule-based game. She agrees to join Jake in exchange for one of his bones (which he no longer needs with his stretchy powers), which she uses to do a reading on herself and see what her future decades will be like. After absorbing the wisdom from her 90-year-old self (and gaining a few wrinkles in the process), she realizes she needs to help Jake with the tournament and returns in time to exorcise his competitive feelings from his 20s. Though they lose the final game, Jake is able to take losing with dignity thanks to Charlie's help, and symbolically "buries" his 20s with Charlie at his side in the final scene. The official art for the episode by Steve Wolfhard also has Lady Rainicorn remark that all the pups are somehow at different ages (hence Charlie being in her 20s, Jake Jr. being "basically 30," Kim Kil Whan appearing more middle-aged, etc.).
Jake was very aware of Finn's previous crush on Princess Bubblegum, so Princess Bubblegum and Jake have a rather strange relationship. They are good friends, though. Jake and Princess Bubblegum rarely speak to each other, but in "Incendium," Princess Bubblegum calls him "puppy" in a sweet, baby voice even letting him rest his head on her lap, and in the episode "Ricardio the Heart Guy" Jake and Princess Bubblegum teased Finn's love for Princess Bubblegum. In "Princess Cookie," Jake stated that he hated her because he thought it was unfair that Princess Bubblegum did not let him be a mailman and made him be a milkman, though it is possible he was just saying this to stall Baby-Snaps. In "Burning Low," Jake misinterprets Princess Bubblegum's attempts at keeping Flame Princess stable as jealousy, and when she returns again looking for Finn, Jake furiously berates her for causing Finn so much emotional pain and for being a "heartless monster." After stabilizing Flame Princess, Jake notices Bubblegum's reaction to Finn and Flame Princess' "kiss" (each kissing a rock to symbolize kissing each other) and mocks her for being jealous, only for Princess Bubblegum to tell him to shut up. In "Too Old," Princess Bubblegum tells Finn that she loves Jake. In "A Glitch is a Glitch", after Finn and Jake disgusted the virus and returned to the candy kingdom, Princess Bubblegum and Jake and Princess Bubblegum's hands say that they missed each other.
Jake and Mr. Cupcake share a rather strained relationship. Jake is worried that Mr. Cupcake will take Lady away from him, so he avoids him most of the time. In the episode "Time Sandwich," it is shown that Jake respects Mr. Cupcake and tries to be like him in some aspects of his life. It is also shown that if Jake were to die, he'd want Mr. Cupcake to look after Lady and their kids, showing a deep trust and respect for Mr. Cupcake.
Jake and Tree Trunks share a close relationship, which is similar to a grandmother-grandson relationship. This is shown most of the time, though there was a situation in the episode "Tree Trunks" when she kissed him several times so that he would let her help Finn.
Jake appeared later with lipstick marks all over his face, and he was smiling. Later, Tree Trunks tells Finn that she'll accept his apology (Finn had earlier yelled at her) if he would let her kiss his cheek.
Finn was about to decline the offer when Jake says "Whoa, let her kiss your cheek, man! It's a once-in-a-lifetime opportunity!" Other than this, there are no references of an unlikely romantic relationship between Jake and Tree Trunks, although they remain close friends. He encouraged her relationship to Mr. Pig and played his viola at their wedding.
In the episode "His Hero," Jake stated he had a secret crush on Billy. And whenever they meet, Jake keeps saying "I love you, Billy!" Jake seems to have great respect for Billy. He quit his "violent" way of saving people and started saving people in a more pacifistic way because Billy thought it was the right way, even though Finn doubts it. In "Billy's Bucket List," it is revealed that Jake is in denial about Billy's death.
Prismo and Jake started hanging out together since the episode "Jake the Dog." They became quick friends and Jake rated Prismo as "A strong number three on my cool guys list." Jake enjoys hanging with Prismo, but implies that Prismo needs a girlfriend because he's so lonely. At the end of the episode, Prismo states that he would like to hang out with Jake more in the future. Their strong sense of friendship was shown in "Wake Up" when Prismo was willing to give up his life in order for Finn and Jake to enter the Crystal Citadel.
Princess Cookie/Baby Snaps
At the beginning of "Princess Cookie," Jake saw Baby Snaps as a villain and a criminal due to the fact he took hostages and wanted Princess Bubblegum's crown. However, he soon befriends Baby Snaps after hearing his story about him and Princess Bubblegum. Jake was happy hearing Baby Snaps stating Jake reminding him of a mailman he knew. Jake even "betrayed" Finn and Princess Bubblegum to help Baby Snaps escape. At the end of the episode, Jake gives him a crown and makes Baby Snaps the princess of the Grass Lands.
After being rejected by Bubblegum again, Finn cannot take it anymore and started sobbing. Jake seeks for a new love interests for him. He then saved Flambo from a group of Iron Owls and asked him if he knows any princesses that is Finn's age. Flambo told him about a "hot" Princess and takes him to the Fire Kingdom to court her. At first, Jake seems to like her as a girlfriend for Finn. However, after she shows her hot-headed side (and her father calls her his "evil daughter") Jake seems to be afraid of her. In "Hot to the Touch," Jake continues to think that she is evil and tries to make Finn understand that. He even suggested Wildberry Princess as an option. As he thought that she was evil, he tried to defeat her and even put out her flames (which hurts her). However, after Finn started to go on dates with her, he started to understand her and no longer sees her as evil and just wanted Finn to be happy.
Jake greatly respects Finn's relationship with Flame Princess and does everything he can to keep it intact, including keeping his distance when the two are spending time together. Jake also defended Flame Princess when Princess Bubblegum apparently attempted to keep the couple apart. He also offers them chamomile tea to show his support of their relationship in "Vault of Bones" when the two were playing cards.
They started hanging out together in "Ignition Point" and interacted more. They seemed to be comfortable around each other. He was also the one who suggests to go back to the Fire Kingdom to get her scented candles.
In "Jake Suit," Jake embarrassed Finn by making him semi-naked and singing the Baby Finn Song in front of Flame Princess and her family members, thinking that would made him win the bet. Unfortunately he did not, as Flame Princess spotted him inside Finn's mouth while talking to him (Finn). She would have yelled at him, but she did not and thought that it was pretty hardcore of Jake of doing this to Finn.
Jake initially has a fear of vampires, which makes him terrified of Marceline. Marceline cannot help it and likes to scare Jake, but in "Henchman," Jake will not accept the fact that Marceline is not evil and almost murders her by exposing her to sunlight.
However, by season two, Jake seems to have accepted that she is not evil and has gotten over his fear of her, although Jake was in Finn's pocket during the events of "It Came from the Nightosphere," and because Marceline attends Finn and Jake's party in "Power Animal" and movie night in "Video Makers." In "Go With Me," Jake announced that he had been learning about vampires lately and that his fear was based on ignorance and even called her to help Finn to impress Princess Bubblegum so that she would go to the movies with him. However, they ended up arguing with each other over the episode.
As shown in "Heat Signature," Jake is now friends with Marceline and visits her house to watch movies. He also is concerned when Marceline is in danger in "Memory of a Memory." They have become close friends, although Jake still holds some level of fear for her, as exemplified in "Marceline's Closet," where he is clearly trembling at the mere thought of what Marceline will do to him and Finn at the realization that they broke into her house and invaded her privacy.
BMO lives with Finn and Jake in the Tree Fort. It serves as their living video game system, film editor, camera, and many more portable electric items. It appeared in the eighth episode of Adventure Time, so it is obvious he has been with them for a long time. In "Video Makers," BMO records the footage requested by Finn and Jake, although they disagree on what genre of movie it will be, so they leave it a note that tells it to keep only the best footage and present it at the Movie Club. It ends up bringing them together by using both the action and comedy/romance footage and singing a song, so it appears it does not take sides with either of them. Occasionally, Finn and Jake seem to take on parental roles when it comes to BMO, such as taking him to soccer practice or disciplining it when it misbehaves.
Jake is fluent in Korean, which he uses to communicate with Lady. A loyal boyfriend, Jake often stops adventuring to make time for her, meeting her every day at 4:00 PM on the dot.
In "Go With Me," they are seen kissing at Couples Only Movie Night. In the episode "My Two Favorite People," Lady recalls a time when she and Jake ran naked through a farmer's field, causing them both to blush. This may indicate some level of intimacy in their relationship, though they are technically almost always naked, aside from Jake's invisible pants.
Jake feels threatened by and becomes jealous when other males are friendly with Lady. For instance, Jake storms off when he misinterprets Finn and Lady's budding friendship in "My Two Favorite People." Another example comes in "Video Makers," when Mr. Cupcake flexes his muscles at Lady Rainicorn instead of acting out a wedding for Jake's romantic comedy movie. Jake says that he told him to say the lines instead of flexing out, who instead responds "I don't hear her complaining," which provokes Jake into attacking him. In "Paper Pete," Jake said that one day he wants to have children with Lady Rainicorn, and at the end of "Lady & Peebles," she tells Jake in English: "I am pregnant!"
Jake is shown in "Up a Tree" to be very devoted to Lady during her pregnancy; he carries the basket while they go out for a picnic, helps roll her up so she can get on the blanket, and later leaves Finn on his adventure so he can walk Lady home. Later, he is shown washing dishes at her house while Finn and the Squirrel fly by. In "All the Little People," he spends 16 weeks at Lady's after being annoyed by Finn's obsession with the little beings. As the pups were born, Jake showed a very high level of dedication towards his family to keep them safe. However, even though they had kids, they showed no thought into getting married and are still technically boyfriend and girlfriend.
In the episode "The Pit" Finn reveals that he is confused whether he should call Jake Lady's husband, or just her boyfriend.Jake also mentions it more throughout the episode like when the girl wants to be his girlfriend he says he already has one and when he sings the love song and again mentions it.
In "The Great Bird Man," Jake reveals he had an ex-girlfriend (whose named was revealed to be Moniker in "Daddy-Daughter Card Wars") before Lady Rainicorn. Jake notes that she was the one that taught him how to read Braille. In "Daddy-Daughter Card Wars," Jake reunites with her and Grand Prix, introducing them to his daughter, Charlie. She still has friendly feelings toward Jake.
The Squirrel considers Jake his enemy, due to the fact Jake did not publish the Squirrel's letter in the newspapers. However, Jake does not seem to remember who the Squirrel is. In "The Duke," the Squirrel (along with the Marquis of Nuts) attacks Jake (along with Finn) at the Grand Meeting of Ooo Royalty (who still cannot remember who the Squirrel is). He returns at the end of "Princess Potluck" when he successfully hits Jake with an arrow, while screaming, "YOU SON OF A BLEEP-BLOB!!! JAKE!!!!" proving that he still has not gotten past his grudge.
The few times Jake and the Ice King are together, they are usually enemies, as seen in "The Eyes" where Jake tries to beat him in battle. However, in "Holly Jolly Secrets Part II" it is implied that both Finn and Jake had "a fleeting moment of empathy" for him. In "Holly Jolly Secrets Part I," the episode prior, the Ice King says "You know how Jake is: 'stretch this stretch that,' blah!" implying that Jake's abilities are rather annoying to him. He was also married to Jake in "When Wedding Bells Thaw," but got unmarried at the end of the episode.
In "My Two Favorite People," Jake calls up a boy named Tiffany and pretends to be best friends with him in an attempt to get Finn and Lady Rainicorn jealous of him. However when Jake makes up with Lady, Finn fights Tiffany and spits on him, causing Tiffany to run away screaming. Before leaving, he vows that he will still become Jake's best friend. He returned in "One Last Job" where it was revealed he lives in a rundown shack, where he idolizes Jake, and was previously part of Jake's old gang. When Jake calls him back, he seems to want to still be Jake's best friend. Jake, however, still does not like him, especially when Tiffany betrays him. Tiffany is shown to be passive-aggressively obsessed with Jake, constantly spouting monologues about how Jake will bow to him, yet pathetically desiring Jake's friendship. Jake mostly seems creeped out by this.
When Jake had a Croak Dream with the Banana Man in it, he was scared of the Banana Man at first. As Jake grew to accept death, his dislike of the Banana Man lessened. Jake thinks that he and Banana Man are destined to meet again when Finn is not around, although he did meet Banana Man again in "We Fixed a Truck" with Finn being there.
Jake and Susan first met in "Susan Strong," where their relationship was pretty friendly. However, after Susan Strong tried to eat the Candy Kingdom, Jake starts to think she is crazy as shown in "Beautopia." Jake constantly repeats that she is insane to Finn throughout the episode, and follows Susan and Finn to annoy and disrupt them.
Gareth was a part of Jake's old gang as described in "One Last Job." Gareth shows greater interest in getting his hands on riches, rather than helping his "friend."
Flying Lettuce Brothers
The Flying Lettuce Brothers were part of Jake's old gang as described in "One Last Job." The brothers show great respect toward Jake, calling him "the master." Nevertheless, they still end up betraying him.
Jake was invite to a party in the Cloud Kingdom and was favored by the Party God for "being a completely off-the-hook party dog." Jake was then allowed one free wish (which was then used to help find Finn) but beforehand figuring out that there was a catch to it.