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Martin Mertens

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This article is about Finn's biological father in Ooo. You may be looking for Farmworld Dad, Finn's adoptive father, or the voice actor.

Martin Mertens (or Martin the Human) is Finn's biological father. Billy calls him "Dad the Human," similar to Finn's title "Finn the Human."


Finn's father was intended to be revealed in "The Lich," as seen in unused storyboard scenes. He was a warrior who was unintentionally trapped in the Crystal Citadel, a prison that is difficult to enter and nearly impossible to escape.

In "Billy's Bucket List," he was officially revealed, albeit briefly. Billy explains to Finn that his human father is trapped in the Crystal Citadel, now renamed the "Citadel." The episode cuts to a brief scene that shows a silhouette of a man trapped in a crystal aboard a massive space station.

In "Escape from the Citadel," he is finally revealed, but has no clear memory of his son, Finn, or why he deserted him. He runs away from the problems at the Citadel as the Lich spreads his evil. He ultimately causes Finn's arm to be removed, as he tries to escape the Citadel while Finn is holding on to the escaping portal, causing Finn's grass sword to take over and remove itself and part of Finn's arm.

In "Astral Plane," it is revealed Martin found a spaceship after the events of "Escape from the Citadel" and was going to crash on Mars. Grob Gob Glob Grod mistook his ship for the Catalyst Comet and sacrificed himself by flying at the comet and sending it on a course for Earth instead of Mars.

In "The Visitor," he is seen to be living with a bunch of villagers and manipulating them to believe in a tree spirit in order to help him build his escape pod. The craft is named 'The Minnie'; possibly the name of Finns biological Mother. Finn is angered with him by the end of the episode for treating the villagers so badly. Finn then pulls a switch on Martin's now fixed escape pod that sends Martin flying into the air, without the roof of the pod closed fully to keep him inside.

In "On the Lam" Martin has made his way to a new planet, once again getting himself imprisoned for betting on "lard-fights." He escaped with a Koala Person who took him to his home with many Koala People. Martin, disliking the food, offered to go to the outside world and get them some real food. This was most likely a lie however, since Martin sold their Space Moth and went to a bar. Martin named the Koala Person, Martin 2 and kept him as a pet. Martin and Martin 2 were recognized by the guards who attempted to capture "the rebel leader." Martin believed this to be him, and attempted to distract the guards away from Martin 2. When it was revealed that Martin 2 was the one they were looking for however, Martin abandoned him, regained the Space Moth and fled the planet.

In "The Comet" after Finn and Jake followed Orgalorg into space in Princess Bubblegum's spaceship, Finn was left floating in space. He was singing a song while Martin found him. Martin almost flaked and didn't save him but he did. Martin need to help Finn stop Orgalorg. Finn spoke to the Catalyst Comet that was going to hit Earth. The Comet gave Finn the option to start a new form of life. Finn declined the offer, but Martin took it up instead. Finn was initially upset with his father for trying to leave him once more but Martin told him, "No answer I give you will be satisfying." and, after being asked why he always runs from everything by Finn, "You burn enough bridges, the only direction to move is forward." Finn accepted that he could never change Martin, and Martin took off with the Comet and said goodbye to Finn. It is unknown if Martin is now a new life form or was brought to a new dimension.

In flashbacks in the "Adventure Time Mini-Series: Islands" episodes, "Hide and Seek" and "Min & Marty" it was revealed that Martin was living on Hub Island (one of the Human islands outside of Ooo). Martin often made bets and got into trouble with people. Martin was also a "hider" (people who would try to leave the islands). After breaking his legs during an unsuccessful escape from the island, Martin ended up in the hospital. Martin was put with a "helper" (doctor) named, Minerva Campbell. Minerva told Martin he had serious concussion. Martin tried to escape the hospital but Minerva caught him red-handed. After this she had to stay overnight at the hospital. At this time Martin was telling her he wanted to date her. She enjoyed hearing this. The next morning several "seeker" (people that would catch people who tried to leave the island) were going to take Martin to "re-education" (a place that convinces hiders to not want to leave). Martin did not want to go to this. Minerva lied to the seekers and told them he was not in condition to go. Luckily the seekers really trusted Minerva and let him stay. After this Martin and Minerva went to dinner and fell in love. After a certain period of time Minerva became a pregnant and gave birth to their son, Finn Mertens. One evening when Finn was an infant Minerva had to go to work. Martin was left alone with Finn and on that night an old foe of Martin broke into their home. Martin ran off with baby Finn and they got on a raft. Martin was planning on just circling around the island but the Island Guardian caught them and Martin and Finn both got lost at sea and did not come back to island and were likely presumed dead.


Martin is a chubby man with a long, dark blond beard, mustache and a mostly bald head, with the exception of a single, curling hair at the top, making him resemble his Farmworld version. In "Escape from the Citadel," he wears a red leotard-type outfit with red spiked shoulders. He has red boots that almost go up to his knees. In "The Visitor," his leotard has been somehow torn, leaving just enough to cover his lower body and his chest is left bare. He also wears a green military-like jacket and his hair in a loose ponytail.

In flashbacks in "Min and Marty", Martin appears to be much slimmer, and has a horseshoe mustache. Throughout all of his attire, he always wears his red boots.


Unlike Finn's selfless and moral personality, Martin is revealed to be an incredibly selfish, lazy, ignorant exploitative and narcissistic individual who barely acknowledges his son's presence unless it benefits him. From the moment he is freed, he is focused solely on saving himself, more shocked at the opportunity of escape than meeting his biological son, Finn. The extremity of his selfishness is shown when he does not even have a reason for abandoning Finn (suggesting he simply left his own baby son to die in the woods without any remorse) he simply says he doesn't remember, even attempting to shift the blame to Finn by saying "maybe YOU left ME," revealing just how immensely immature Martin is.

Martin is also a very emotionally barren person. He has absolutely no empathy and does not seem to understand how his actions affect others, such as treating Finn's emotional attempts to bond with little more than irritation and ingratitude. He then proceeds to manipulate Finn into fixing his leg by baiting him with paternal affection. Once his leg is fixed, he once again abandons Finn, completely unconcerned that Finn loses his arm in a desperate attempt to stop him. He also showed a total lack of sympathy for one of the collapsing Citadel Guardians. Finn at one point reflects that maybe Martin "isn't a dad, but a kid in a dad's body." Further evidence of this is shown in Martin's later appearances, his childishness suggested in his obliviousness to the total cruelty of some of his actions, such as trying to hug Finn right after lying to him about losing his arm, or putting Finn into a leglock to avoid the awkward silence that came after the half-hearted explanation of Finn's abandoning. 

However, like Finn, he is shown to be very persuasive, as he was able to convince the other escaped convicts to make him their leader. Martin does this using the same falsely charming smile and wink he used to get Finn to help fix his leg, emphasizing that, to Martin, others are just interchangeable assets to be exploited or manipulated for his own survival or gain and his son is no exception. 

In "The Visitor," the Martin's manipulative and utterly insensitive nature is further explored. When he called Finn into the tree that he had been living in, he faked losing an arm to gain Finn's sympathy so he could avoid his son's own speculated anger about losing his own. This innate cruel streak in Martin is also signified when he exploits the locals, making them build him a new ship that he would use to escape his crashed ship's explosion. He also spits out feathers while eating a bird's egg, implying that he was eating a hatch-ling.

In the same episode, it is confirmed that Martin really is Finn's father, and that talking about Finn's mother stresses him out, suggesting that whatever caused their separation was traumatizing. At some point, he made a choice that made him leave Finn behind, though he says he always intended to come back for him.

During the flashback in "Min and Marty", Martin was more or less similar to his current self, but developed better traits through his relationship with Dr. Minvera Campbell. As a father, Martin is shown to be loving and caring person towards both Minerva and their infant child, Finn. Prior to meeting Minerva, however, Martin was spending his time as a con artist, selling out others in exchange for "gadgets". This checkered past of his ultimately comes back to spite Martin when he and baby Finn are chased off the island.

Issue about parenthood

Meeting Finn Mertens' birth father is a situation the boy can’t deal with by swinging his sword at a "bad guy," so this issue keeps him unable to move forward. When Finn finds out that The Citadel is a prison, he naively assumes that Martin is the warden. Finn’s reluctance to draw negative conclusions about his absent parent sets him up for major disappointment when they reunite.[1]

Martin appears to be a darkly comic subversion of most absent parent storylines seen in cartoons or even anime; when the child is finally reunited with the parent, they often find out the parent left or abandoned them unwillingly in order to protect them from something or in the service of some greater cause. It is revealed in "Min and Marty", that Martin didn't intend to abandon Finn, with their separation being a result of a combination of unforeseen consequences. Finn's insecurity about being abandoned combined with his view of Martin created both sadness and hatred in Finn, an issue that was shown in the episode "The Tower."

In "On the Lam," Martin's recollection of the events eventually shown in "Min and Marty" hinted at his now-lost parental personality, showing that when Finn was a baby Martin fought to protect him.

Episode appearances

Major appearances

Minor appearances

Mentioned or pictured


  • He is very resistant to pain, like his son, Finn. When he is shot by a laser from a Citadel Guardian in his leg (causing it to melt his flesh, only shows bone), he says, "It's okay. It's okay."
  • He is also talented at climbing and swimming, as he was able to climb a long vein and swim through the molten center of the Citadel.
  • Like his son, Finn, he is incredibly persuasive, convincing the ancients (Demons that have committed cosmic crimes) to make him their leader.


  • Martin originally was supposed to appear in "The Lich" after Billy told Finn about him; however, the postmortem spirit of Billy eventually tells Finn about Martin's existence in "Billy's Bucket List."
  • As seen in the original storyboard of the episode "The Lich" in the scene 118/panel C, it's possible to read in the description of the holographic animation about Billy's hands pulling Martin to the Crystal Citadel, presuming that Billy knows about Finn's dad because he was the one who put him in the Crystal Citadel.
  • Jake is shown to dislike Martin, referring to him as a "loser."
  • Martin's beard looks similar to the elderly Finn's beard in "Puhoy."
  • Martin's final words before disappearing into the void were "Hey, what about air?" implying that he cannot survive in space like the ancients and may have possibly died upon entering the void. This was confirmed to be false at the end of "Astral Plane."
  • Since his first appearance, Finn was shown to hate Martin, even attempting to take his arm as revenge for losing his own in "The Tower," though Finn still refers to Martin as his "dad," but in an unfriendly way.
    • However, Finn no longer despises Martin, but doesn't necessarily like him either. He now calls him 'Martin' more often than 'dad.'
  • In "The Comet," he states that he can't keep track of time consistently as he "doesn't have a star to revolve around," implying that he spends more time outside of Earth than he does on it.
    • In the end of the episode, he technically no longer exists. It is unknown if Finn considers him dead, or if his departure with the Comet is even considered death.
  • As this moment has been waited for a long time, some fans were disappointed by how much of a jerk Finn's father is but Jeremy Shada says, he is content about this because it makes the show seem more realistic.
  • In the episode "Don't Look," it can be noted that Finn's monster form resembles the physical traits associated with his father, indicating that Finn potentially associated the negative traits mentioned in the episode with that of Martin's attributes.
  • In "Min and Marty", Martin is told by Minerva that he has psychological problems, though he is already aware of them.
    • He also suffers two head injuries in the duration of the episode, the first was a concussion from hitting his head on his hospital bed, and the second caused by his damage to the Guardian. These head injuries combined with his already present issues is likely what caused him to become the sociopath he was at his debut.
      • In the promo art made by Sam Alden, the extent of Martin's injury sustained by the Guardian is shown. It's most likely that the head injury caused permanent brain damage and is largely responsible for his personality and memory issues
    • The episode also reveals that he was still a con artist when living on the Island, though he became a barber after meeting Minerva.
    • In the episode "The Visitor", Martin's escape pod is named The Minnie.

Cultural references

  • Martin's red leotard is likely a reference to Sean Connery's various ridiculous and revealing red outfits in the 1974 science fiction film Zardoz.



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