Finn the Human 

Finn is the show's main protagonist, a brave and enthusiastic human boy who loves to go on adventures and help anyone in need. He is the last human in the Land of Ooo for much of the series. He lives in a treehouse with his best friend and adoptive brother, Jake. While he starts as a young boy, he matures throughout the show, grappling with complex emotions and his own identity.

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Jake the dog 

​Jake is Finn's best friend and adoptive brother. He is a dog with magical stretching powers that allow him to change his body into any shape or size. Jake is a laid-back and wise-cracking character who acts as Finn's older brother and mentor, though his advice can be unconventional. He is in a relationship with Lady Rainicorn and they have five children together.

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Princess Bumblegum 

Princess Bubblegum, or Bonnibel, is the ruler of the Candy Kingdom and a brilliant scientist. She is made of living bubblegum and is over 800 years old, though she maintains the physical appearance of a young adult. She is kind and compassionate, but also fiercely protective of her kingdom and can exhibit a more authoritarian side when she feels her subjects are in danger. She has a complex history with Marceline the Vampire Queen.

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Marceline the Vampire Queen 

​​Marceline is a 1,000-year-old half-demon, half-human vampire who is also a talented musician. She is known for her cool and mischievous personality and for floating rather than walking. Despite her intimidating title, she is a close friend to Finn and Jake. Her backstory reveals a deep and meaningful connection to the Ice King from before he became insane, and a tumultuous but ultimately loving relationship with Princess Bubblegum.

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Ice King 

The Ice King, whose real name is Simon Petrikov, is an ancient wizard who can control ice and snow. Initially portrayed as a bizarre antagonist who constantly tries to kidnap princesses, his character is later revealed to be a lonely and tragic figure. He was once a human antiquarian who was driven to insanity by the magical crown he wears. His madness has made him forget his past, including his fiancée Betty and his close friendship with a young Marceline.

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Lumpy Space Princess (LSP) 

LSP is a melodramatic, self-obsessed, and sarcastic princess from Lumpy Space. She often acts like a stereotypical valley girl and is the source of many of the show's comedic moments. Despite her seemingly selfish nature, she has a good heart and undergoes a significant heroic arc, demonstrating compassion and even saving the Land of Ooo.

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BMO 

BMO (pronounced "Beemo") is a living, sentient video game console that lives with Finn and Jake. BMO is their friend, roommate, and companion. BMO is a kind and gentle character with a child-like personality, and is often shown doing various activities with Finn and Jake, from playing video games to helping them with their quests.

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