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

You burn enough bridges, the only direction to move is forward.

—Martin in "The Comet"

Martin Mertens, also formerly known as Mr. M, is Finn's biological father. Billy calls him "Dad the Human", similar to Finn's title "Finn the Human".


He was first revealed in "Billy's Bucket List", albeit briefly. Billy explains to Finn that his human father is trapped in the Crystal 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 large group of small 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'; the nickname of Finn's 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 was close to leaving Finn, however ultimately decided to help him. Martin believed he needed to help Finn stop Orgalorg, strangely considering his cruel nature. Finn managed to have a long and meaningful conversation with the Catalyst Comet that was going to hit Earth. The Comet gave Finn the option to start a new form of life, traveling with The Comet for all of eternity, however Finn declined the offer to stay with his friends. 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 Islands episodes "Hide and Seek" and "Min and 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 a con-artist. He at one point tricked the "hiders" (people who would try to leave the islands) into thinking he knew a way past the seekers. He tried to not go with the hiders, however, they forced him to go on the escape with them. 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 a 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 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, thinking that they were trying to leave, caught them. Martin told baby Finn he that he'll be back for him and went on to attack the Island Guardian. Using a laser gadget, he blinded the Island Guardian's left eye, the Island Guardian then created a big wave and Martin and Finn, still separated, both got lost at sea and did not come back to the island.

In the Adventure Time: Distant Lands episode "BMO," set prior to the events of the parent series, BMO encounters someone going by the name of Mr. M, who is heavily implied to be none other than Martin Mertens: he displays the same selfish tendencies of Martin, says things like "Here comes the rascal" and "I gotta get the heck out of here," and at one point remarks that kids always call out parents on being deadbeat.

In the spin-off sequel series, Fionna & Cake, Martin is briefly seen on Scarab's list of fugitives in the episode "Prismo the Wishmaster", wanted for "DESERTION". An alternate version of Martin appears in the episode called "The Star" and is seen with alternate versions of Princess Bubblegum and Huntress Wizard in a Vampire Universe where they're all Vampire Hunters. Unlike his main-timeline counterpart, this version of Martin seems to be less cowardly and selfish. When Fionna, Cake and Simon Petrikov join the vampire hunters, they see that Baby Finn has tagged along and Martin seems to love his alternate son. Unfortunately, Martin was killed and his soul was sucked by The Star, an alternate version of Marceline.


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.

In the Adventure Time: Distant Lands episode "BMO," Martin, as Mr. M, wears a black, long-sleeved leotard with light grey tights underneath, light grey gloves, black anti-gravity boots, a grey shawl, and a round, black helmet with a circular, red display infront of it. The display visually animates Martin's vocalizations, and shows a thin, white "M" when he is not speaking.


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 reconnecting with his biological son, Finn. The extremity of his selfishness is shown when he does not even provide a reason for abandoning Finn, simply saying he doesn't remember, even attempting to shift the blame to Finn by saying "maybe YOU left ME," revealing just how immensely immature and uncaring 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.

Like Finn, Martin is shown to be very persuasive, as he was able to convince the other escaped convicts to make him their leader. He 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," Martin's manipulative and utterly insensitive nature is further explored. When Finn approached 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 Villagers, making them build him a new ship that he would use to escape his previous ship's crash site with no regard to their safety. He also spits out feathers while eating a bird's egg, implying that he was eating a hatch-ling.

Finn at one point reflects that maybe Martin "isn't a dad, but a kid in a dad's body." Evidence of his childishness is 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.

In the same episode, it is revealed 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, even displaying some of his current tricks, such as his wink and smile (which he tried and failed to use on Kara) and his war cry "Heres comes the rescal!" (used in "On the Lam"). Martin was spending his time as a con artist, selling out others in exchange for "gadgets." It's even implied that Martin initially tried to use his charm on Minerva Campbell to avoid re-education. However, as the relationship between the two developed, he developed better traits. As a father, Martin is shown to be a loving and caring person towards both Minerva and their infant child, Finn. He also set himself on a better path, working at a barber shop instead of conning others. Martin's checkered past of his ultimately comes back to spite him when he and baby Finn are chased off the island.

Relationship with Finn[]

Finn meeting his father represented a new challenge for his character, one that couldn't be dealt with by swinging a sword. In this way Finn's evolving relationship with Martin helped demonstrate Finn's maturation throughout the series, going from child-like certainty about his father's goodness[2], to intense hatred, to simmering resentment, to ultimately accepting Martin as a flawed individual and a product of his own circumstances.

Martin appears to be a darkly comic subversion of most absent parent storylines seen in fiction; when a child is finally reunited with their long-lost parent they often discover the parent was forced to leave them for some greater purpose. Instead of a noble sacrifice, Martin was simply separated from Finn at a chaotic moment, assumed his son was lost, then deserted his old life rather than face the consequences.

Finn imagined meeting his father would be the end of most of his life's mysteries. Instead, in the aftermath of their meeting and escape from the Citadel, Finn became consumed with newfound resentment and insecurity regarding Martin. These feelings briefly consumed Finn, to the point of seeking revenge against Martin, as 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 (Beings that have committed cosmic crimes) to make him their leader.


  • Martin was originally supposed to appear in "The Lich" after Billy told Finn about him; he was a warrior who was unintentionally trapped in the Crystal Citadel, a prison that is difficult to enter and nearly impossible to escape. 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".
  • 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.
  • In "BMO" Martin (disguised as Mr. M), said "Well, Here comes the rascal", similar to when he said "Here comes the rascal!" in "Min and Marty".
    • In the same episode, he also says “Ha. Kids, right? Always calling out their deadbeat parents.”, most likely in reference to him abandoning Finn.

Cultural references[]

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


Official art[]