Humans (or Homo sapiens sapiens) are a critically endangered species in the Land of Ooo. It is hinted that they were driven to near-extinction roughly a thousand years before the events of Adventure Time, during an event called the Mushroom War, a global thermonuclear war.
Many residents of the Ooo are under the impression that humans no longer exist as demonstrated by Bob and Ethel Rainicorn in "Her Parents." Due to their rarity, many characters marvel at Finn's humanity, such as Princess Bubblegum in the episode "Susan Strong."
There are several other beings that resemble humans in the Land of Ooo, such as Penny, Phil or the Old Man Henchman. Despite their resemblances, most of these beings are not recognized by other characters to be humans. According to the show's writers, these characters should be referred to as humanoids or mutants. Some of these beings, however, were actually humans in the past, which includes Ice King, Business Men, and Moe. The old ladies scattered around Ooo from "The Enchiridion!" and "Be Sweet" are very human like but are actually a species of old ladies, as revealed in "Thanks for the Crabapples, Giuseppe!"
Finn was the only confirmed human until the episode "Betty," when Simon accidentally brings Betty into the future, and in "Billy's Bucket List," when Finn's father, is confirmed be alive. It is confirmed in "Dark Purple" that Susan Strong is indeed human. However, she seems to have cybernetic implants in her head, implying that she is not entirely human. Later, in "You Forgot Your Floaties", Betty became a Wizard by using Magic Man's powers, so she is now no longer fully human.
In "The Comet," Finn was given the offer from the Comet to take a new form. Finn declines but Martin decides to take it making him a cosmic entity, likely making him no longer human.
In "Everything's Stays," a tribe of humans were seen departing the continent of Ooo on a patched-up pre-war ship. It is unknown if this tribe still exists, or if they even managed to leave Ooo. It is probable that these humans are the hyoomans before their mutation or their ancestors, due to their similar attire.
In the episode "Preboot," Susan's implant has something to do with Doctor Gross, and that until this point, were deactivated. When they became activated due to electricity in "Reboot," she speaks in a robotic-sounding voice and attempts to take Finn to the edge of the ocean, claiming he is her "objective." While in this state, she is able to absorb the blast from a Gumball Guardian and make herself larger. At the end of the episode, Finn destroys the cybernetic implant and Susan returns to her former self, becoming wholly human in the process.
In the mini-series Islands, it is revealed that a large population of lost Humans are located southwest from Ooo and settled in three (previously four) islands but most of them are on Founders Island. During the Mushroom War, humanity was on the brink of extinction until they were saved by The Founders (one them being Two Bread Tom seen in the episode "Hide and Seek"). They were brought to the islands, where they lived isolated from the rest of the world and did not allow anyone to leave the islands and had a robotic Guardian prevent anybody from leaving (or coming in). At some point in time (hinted to be around 700 years ago) the humans had a catastrophic event as said by Minerva and Dr. Gross said that the humans once tried to explore the outside world and were almost destroyed. However, it is not clear if these two events described are the same occurrence. After another 300 years, Dr. Gross accidentally released a virus that slowly began to destroy humans. In a desperate attempt to save humanity again, a Helper named Minerva Campbell became an artificial intelligence that commanded hundreds of robotic bodies that aided the surviving humans on Founders Island ever since until Finn, Susan, Jake, and BMO found the remaining human population and convinced them that the outside world is not all dangerous. Even though the only human who ended up leaving the islands was Susan's old friend Frieda, the humans now have the freedom to leave the islands and the guardian was deactivated. So after "Islands", Finn's status as "the last human" was completely debunked.
- Finn Mertens
- Susan Strong (formerly had cybernetics implanted in her head before they were removed by Finn in "Reboot")
- The Thousands of Humans of Founders Island
- The Many Better Reality Players
- Marceline (Human/Demon hybrid; later a vampire)
- Dr. Gross (Human/Cyborg hybrid; claims to be an enhanced human)
- Stormo (Human/Candy Sphinx hybrid)
- Jay & Bonnie (Human/Pillow hybrid)
- Fern (Human/Grass Person Hybrid)
- Marceline's mom (presumed)
- Moe (Human, with cybernetic implants)
- Abraham Lincoln (cosmic entity, as revealed in "Orgalorg")
- The huge majority of the 7 billion humans that populated Earth before the Mushroom War
- Two Bread Tom
- Bunny Girl
- Most of the humans of Hub Island
Known former humans
- Simon Petrikov (currently a wizard)
- Minerva Campbell (currently an A.I.)
- Betty Grof (currently a wizard)
- Martin Mertens (likely currently a cosmic entity)
- Business Men (currently mutants/zombies)
- Patience St. Pim (possibly currently an elemental)
- Flynn (Fionna's Genderswap)
- Commander and Private (fictional animated characters from Heat Signature)
Humans from the Farmworld timeline
- Finn Mertens
- Finn's mom
- Finn's dad
- Finn's baby brother
- Choose Bruce
- Destiny Gang
- The use of coifs by the humans is used for protection from vampire bites, as revealed in "Everything Stays".