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Abraham "Abe" Lincoln was the King of Mars who debuts in the original animated short, where he encourages Finn to believe in himself after warping his brain in the past and to Mars. His first appearance in the official series is in one of the framed pictures in Hunson Abadeer's house. Lincoln plays a major role in the episode "Sons of Mars," where he loses his immortality (and seemingly his life) in order to save Jake after he was accidentally killed and sent to the 37th Dead World. As a result, Lincoln turns to stone, and becomes a statue for all of eternity.
Abraham Lincoln is a notable figure outside of Mars and many refer to him on Earth. In "Business Time," Lincoln is seen as a character included in a game on BMO. He is mentioned in "Crystals Have Power," when Jake states, "If I had a penny for every time someone went crazy hopped up on magic energy... I'd be Abraham Lincoln!" He is also referenced in Issue 3 of the Adventure Time comic. When Finn is telling everyone how to beat The Lich, he says that just like Abraham Lincoln said in the past and on Mars, "you need to believe in yourself," however it is highly unlikely that he intended to quote Lincoln.
Abraham Lincoln is modeled closely after the real-life Abraham Lincoln. He wears a black suit with a black bow tie. Two major differences from his real-life appearance are that, in the show, he has the ability to float, like Marceline, and he has a yellow light surrounding his head (only in the animated short). He also doesn't wear his famed stovepipe hat. Unlike most characters, his hands have five fingers. He sits atop a throne that is engraved with the symbol ♂, the astrological symbol of Mars, which has come to also represent "male" in contemporary popular culture. This symbol can also be found in the arena in which Lincoln sits nearby at.
Lincoln speaks in a colloquial vernacular of the late 20th century, much different from his published speeches in the 19th century. He uses phrases such as "bums me out" and "I remember when you were really cool" and is extremely expressive and emotional, especially during his sentencing of Magic Man. He is not without subtlety, however, such as the private joke he shared with Death.
If you had just learned to care about living things again you could have come back whenever you wanted, instead you bummed around Ooo acting like a jerk for 200 years.
—"Sons of Mars"
Magic Man I give you two choices: one is total annihilation. The wand will touch you and your soul will meet with Death; the second is to use the power of the wand to convert your body to living stardust where your consciousness will be jettisoned in the infinite cosmos on an endless journey of wonder and discovery!
—"Sons of Mars"
- "Animated short" (debut)
- "Business Time" (video game)
- "Crystals Have Power" (mentioned)
- "Return to the Nightosphere" (photo)
- "Box Prince" (video game)
- "Orgalorg" (flashback)
- "Normal Man" (flashback)
- Rebecca Sugar has stated the she thinks of Abraham Lincoln as the equivalent of Jesus in Ooo. However, according to Adam Muto, he is more of a "recognizable figure," while adding that it would be "a stretch to call him a religious figure." 
- He has a very detailed face, unlike most Adventure Time characters. But in season 4 he appears to be not as detailed as he is in the animated short.
- It is implied that Abraham Lincoln has bargained for a soul with Death in the past. He uses a penny as barter, similar to how the dead ones were transported through the river Styx to Hades.
- In "Sons of Mars," both Grob Gob Glob Grod and Magic Man refer to the land as Earth since they are Martians. However, Abraham Lincoln, the King of Mars, still refers to it as Ooo.
- As of "Sons of Mars," he becomes a statue, that resembles the one inside the Lincoln Memorial in Washington D.C.
- When Abraham Lincoln sacrifices his immortality to Death in "Sons of Mars," a gunshot can be heard as the screen fades out. This references the actual death of Lincoln by his assassin, John Wilkes Booth.
- In "Business Time," there are two Abraham Lincolns playing football with each other in BMO's game.
- Abraham Lincoln's coat and bow tie have changed color since the animated short.
- Abraham Lincoln is one of only several characters to have five fingers as opposed to the usual four.
- Abraham Lincoln's face appears very briefly in "A Glitch is a Glitch."
- It is unknown what species he is. Finn (who at the time was not known to have met any other humans) did not ask or seem to wonder if he is a human. He appears as a human (as he was in real life) but may be an cosmic entity, deity, or mutant who appears as human. So can say due to his giant size he is not a normal human and is likely a cosmic entity appearing as one.
- Abraham Lincoln on Wikipedia