Adventure Time is an American animated television series created by Pendleton Ward. The series follows the adventures of Finn, a 14-year-old human boy, and his best friend Jake, a dog with magical powers to change shape and grow and shrink at will. Finn and Jake live in the post-apocalyptic Land of Ooo. Ward describes Finn as a "fiery little kid with strong morals", while Jake is based on Tripper Harrison, Bill Murray's character in the movie Meatballs.
The show is set in a fictional continent called the "Land of Ooo", in a post-apocalyptic future after a nuclear war called the "Great Mushroom War." According to Ward, the show takes place "after the bombs have fallen and magic has come back into the world". In "The Real You", when Finn wears the Glasses of Nerdicon, planet Earth can be briefly seen from space, with a large chunk missing from it. Later it is shown in the episode "Five Short Graybles," which initially shows the storyteller with a rotating holographic globe with a portion missing, where the North American continent would be. In "Sons of Mars", this depiction of planet Earth is again presented, but this time, not fleetingly like in previous episodes. During a presentation at the Toronto Comics and Arts Festival, Ward said that this will likely never be directly addressed in the series.References to the war are shown constantly in the show. The first two seconds of the opening credits show nuclear bombs, melee weapons (such as swords and axes), abandoned human items (such as a TV set, headphones, cassette and video tapes) are scattered everywhere, even a skull on the ground. In "Ocean of Fear", when Finn and Jake are out in the middle of the ocean, there is a tank on the small patch of land they swim to. Later on, when they swim to the bottom of the ocean, there are a many sunken cars and tall sunken buildings. When Jake and Finn fight the Lich in "Mortal Recoil", they do so in an abandoned subway station. In the episode "Memory of a Memory", when Finn gets into Marceline's childhood memory, The background is of a city with broken bridges, building which are on fire. There are also tanks and home furniture.The war's effect on humans is also shown, with there seeming to be no other fully human character except for Finn. However, human remains are scattered all around Ooo. Also, in "Beautopia," a character by the name of Susan Strong is implied to be human as well, although it is unclear whether she is really human or she belongs to a strange fish-headed, animal-hatted mutant tribe. In "Holly Jolly Secrets", Finn and Jake discover a few secret VHS tapes by the Ice King, where the last tape shows Ice King as a human. In the tape, he explains he purchased his golden crown from an old dock worker in northern Scandinavia.
- Finn the Human (voiced by Zack Shada in the pilot short where his name was Pen, by Jeremy Shada in the TV series) – Finn is a 14-year-old human boy who loves nothing more than going on adventures and saving the day. He wears a self-proclaimed 'awesome hat' that covers his extremely long flowing golden hair (which he cuts off in "To Cut a Woman's Hair" and is seen to progressively grow back in following episodes). He is prone to exclamations and outbursts including "Mathematical!" and "Algebraic!". When Finn was a baby, he did a 'boom boom' leading to his adoption by Joshua and Margeret (Jakes parents), which we find out in 'Memories of Boom Boom Mountain'. Considering himself a hero, Finn has a lust for adventure and swore long ago that he would help anyone in need, but being so full of energy, he has trouble in situations that require him to do tasks other than fighting monsters. He has some fears, such as the ocean, clowns, and being judged by older people due to his age. He is the main protagonist of the show and likely takes his name in the short, Pen, from the show's creator, Pendleton Ward.
- Jake the Dog (voiced by John DiMaggio) – Jake is Finn's best friend and adoptive brother. He is a 28-year-old (in "magical dog years") shape-shifting dog. His magic powers allow him to stretch or shrink any part of his body to any shape and almost any size, ranging from becoming gigantic to becoming incredibly small. Acting as a confidant and mentor to his energetic brother (though he has a tendency to give somewhat sketchy advice), Jake has a laid-back attitude in most situations, but loves adventure and will eagerly fight when he needs to. In the episode, "The Apple Thief", it is revealed that Jake used to steal bikes and purses from old ladies. His powers help Finn considerably in combat and transportation, but are also sometimes used as nothing more than jovial forms of expression. Jake is currently dating Lady Rainicorn, who is now pregnant (which was revealed in "Lady and Peebles") with what might be Jake's puppies. He met Lady in the pilot episode and is quite skilled at playing the viola, which houses a worm called Shelby.
- Princess Bonnibel Bubblegum (voiced by Paige Moss in the pilot short, Hynden Walch in the TV series, Isabella Acres when turned younger) – Princess Bubblegum is a bubble gum humanoid, comparable to the inhabitants of Candy Kingdom, of which she rules, who are all composed of types of desserts and candies. Her proficiency in science and fluency in Korean and German are a testament to her high intelligence. While Princess Bubblegum is typically kind and well-mannered, her temper can be a powerful force when provoked. Marceline reveals that Bubblegum's first name is "Bonnibel" in "Go with Me". In "Mortal Folly", she admits that she cares about Finn and gives him a sweater she knitted to keep him warm, and in "What was Missing," it is implied that she and Marceline may have had some sort of relationship in the past. In the Season 2 finale "Mortal Recoil", after being possessed by "The Lich", she is accidentally shattered and returned to life as a 13-year-old due to the doctors not having enough gum to work with, though it appears that her memories have remained intact. In "Too Young," she becomes 18 again by absorbing the parts sacrificed by her candy subjects in order to reclaim her kingdom from the Earl of Lemongrab. In season 4, "Goliad", the events have shown to have an effect on Princess Bubblegum, as she begins to feel very vulnerable, and makes a clone-Sphinx of herself named Goliad.
- Lady Rainicorn (voiced by Dee Bradley Baker in the pilot short, Niki Yang in the TV series) – Lady Rainicorn is a half-rainbow, half-unicorn creature and Jake's girlfriend. She can turn objects and people different colors. Her origins can be traced back according to the episode "Her Parents," in which Jake explains how rainicorns and dogs have been battling over the Crystal Dimension for centuries. The episode also alludes to Rainicorns having a taste for human flesh, when her parents attempt to eat Finn, however Lady herself has never shown hostility toward Finn and always has a kind disposition with him. She can fly because her body intercepts light and can dance on it, which also explains her movement and why she has a rainbow pattern. Jake describes her as "the Rowdy Queen" because she can have fun and fight evil. In the pilot short, she makes pigeon-like sounds to communicate, but in the TV series, she speaks Korean. In both cases, despite being unable to speak the major language depending on the dubbed versions, she is able to understand it. As the TV series goes on, especially after "Her Parents," Jake and Lady's relation continue to grow, and in the end of the episode "Lady and Peebles," it is revealed that Lady is pregnant.
- The Ice King (voiced by John Kassir in the short, Tom Kenny in the TV series) – The Ice King is the main antagonist of the series who is around 1,000 years old. The Ice King frequently steals princesses throughout Ooo to forcefully marry them, Princess Bubblegum being his usual target. His magic abilities to freeze things by hurling frozen lightning bolts, summoning snow monsters, and flying with his beard come from the magical crown he wears. He is a master of the martial art of Frijitsu, a technique calling upon the power of ice. Though defined as a sociopath by many, the Ice King is actually lonely and misunderstood, having a generally benevolent relationship with the penguins (primarily one named Gunter), along with the snow and ice beasts who populate his realm, and secretly envious of Finn and Jake for being such good friends. Ice King's origins are revealed during the events of "Holly Jolly Secrets" when one of his home-video movies showed that he was originally a human antiquarian named Simon Petrikov who was taping a documentary of a crown he bought from an old dock worker in northern Scandinavia, predating the Mushroom War. Wearing the crown, Petrikov begins to lose both his mind and then his fiancée Betty, the source of his subconscious need for princesses, deteriorating in both mind and body over the years into his current state.
- Marceline Abadeer the Vampire Queen (voiced by Olivia Olson) – Marceline is a fun-loving and mischievous 1,000-year-old vampire Queen. Marceline plays an electric bass, which she made from her family's heirloom battle-axe as revealed in "It Came from the Nightosphere", and occasionally plays musically with Finn and Jake. Unlike most vampires, she reveals that it's the color red she likes to suck out of various things, and blood is only appealing because it is red. Like a traditional vampire, she is vulnerable to sunlight and is capable of turning into a bat, varying in size. The show generally portrays her as a close friend of Finn and Jake, but she often feels alone as depicted in "Marceline's Closet". It was also revealed in "Return to the Nightosphere" and "Daddy's Little Monster" that her dad desired Marceline to be the next in line to rule the Nightosphere, however she does not want to take up the position. She is a survivor of the "mushroom war" as stated by series creator Pendleton Ward, and in "Memory of a Memory" a trip into Marceline's mind shows her as a child wandering around the outskirts of a destroyed city. Marceline is the only person to ever address Princess Bubblegum by her first name, Bonnibel, in "Go with Me?" . In "What was Missing," it is implied that she and Bubblegum may have had some sort of relationship in the past. While Marceline has many things in common with Finn, in the episode "Go with Me?" and "Daddy's Little Monster" it was stated that Marceline likes Finn for being 'just' himself, and nothing more or less.
- Lumpy Space Princess (voiced by Pendleton Ward, the show's creator) – Lumpy Space Princess (or "LSP" for short) is the princess of Lumpy Space, an alternate dimension. Like all her people, LSP is an extraterrestrial creature known as a "Lumper" which looks like a floating purple cloud with arms and a face, and can convert other beings into Lumpers by biting them. LSP is spoiled and sarcastic, constantly seeking to improve her appearance from getting cosmetic surgery to punching herself into a ball in order to be less lumpy. In later seasons she is shown as being proud of her "lumps" and makes it known on more than one occasion that her lumps are the source of her attractiveness. She is often shown living outdoors with salvaged furniture and appears to be homeless, because she has either run away from home, or is seeking independence from her parents. She speaks with a thick (albeit masculine) Valley Girl Accent. Her parents are the king and queen of Lumpy Space. It appears that LSP can only float above the ground and cannot fly, although she can turn this off by touching the star on her forehead. LSP's relationship to Finn and Jake has always come off as nonchalant, however in the episode "Gotcha", LSP realizes that Finn is a person of good moral standing who teaches her that beauty comes from the inside, and in her premier episode she reveals to Finn that he's supposed to be her real friend, not like the "fake" ones she has in Lumpy Space.
- Beemo (voiced by Niki Yang) – Also known as BMO, Beemo is a sentient video game console that lives with Finn and Jake. Beemo is genderless. It appearance contains elements of Vectrex, Game Boy, PocketStation and Atari 2600 game hardware. Beemo also has the features of other household objects, such as a camera in "Conquest of Cuteness" and a VHS player and alarm clock in "Holly Jolly Secrets". Beemo's "face" (front panel) can be removed in order for its synthesizer to be played manually as revealed in "What is Missing". The letters on it side spell "BMO", but it has never been stated if this actually stands for anything. Beemo can transport people into a video game by pressing a button on its face, but the button only works if Beemo is the one to press it, as revealed in "Guardians of Sunshine". Beemo speaks English with an East Asian accent. In the episode "Five Short Graybles", it was implied that Beemo secretly performs human-like actions like brushing its teeth, possibly in an attempt to try and see what being "a real boy" is like. While Beemo is an object used for recreation on Finn and Jake's parts, it is still considered a close friend and treated as an equal by the two.