Finn

Finn (known as Pen in the original short), along with Jake, is the main protagonist of the series.

Background
Finn was born to unknown parents and was orphaned at a young age, as shown in Boom Boom Mountain, when Finn reveals he took a "boom boom" on a leaf and fell in it. As he lied there, crying, no one bothered to help him until Joshua and Margaret, two dogs, appeared. Ever since then, he has vowed to help people in need of assistance. It is unknown when he met Jake, but it is likely that Joshua and Margaret adopted him and Jake was their son. In memories on Boom Boom Mountain he and Jake call each other brother many times, but this may be a coincidence.

Appearance
Finn is a 12 year old human being with very thin limbs and wears a white hat that covers all except his face with two "ears" sticking out on top. He also wears a blue short-sleeved shirt, blue-jean shorts, a backpack made up of two shades of green, and a pair of black shoes. When he speaks, you can see that he has several teeth missing.

Personality Finn is brave and, as revealed in The Enchiridion, is righteous, due to him slaying only evil things. He often shouts random phrases such as "Shmowzow" and "Holy-Cow", along with many other nonsensical terms.

Personality
Finn has an incredible sense of responsibility and get very upset when he is unable to help others. This is due to his traumatizing events as an infant shown in Boom Boom Mountain.

Abilities
Finn is proficient in hand-to-hand combat, as well as several other tactics. Finn also has some oragami skills, as show in Ricardio The Heart Guy where he makes Princess Bubblegum a paper crane. Finn might still have his many "magics" because in wizard it is never actually said that he loses them. He can auto-tune his voice at will because he has sometime in the past eaten a small computer, as show in jiggler.He can fold very far flying paper airplanes, as show in enchiridion. He is very good at playing a game called adventure master, which he beats in buisness time.

Relationships
Being a hero, Finn has become quite popular in the Land of Ooo, starting many relationships.

Jake
Finn and Jake are best friends and will go out of each other's way to protect each other, no matter what. Finn becomes visibly angry whenever Jake is hurt or presumably dead. This relationship existed from the start of the series. Jake seems to call him 'brother' and 'dude' often, showing that they share a brotherly relationship. However, Finn can get frustrated with Jake because of his laziness, shown especially in The Witch's Garden when Finn yells at Jake because he wasn't even trying to regain his powers. Finn has been frustrated with Jake before, such as in the City of Thieves when Jake, overpowered by the thievery of everyone around him, steals a pair of boots.

Lady Rainicorn
Finn became friends with Lady Rainicorn after Jake wanted to hang out with both of them at once. This backfired on Jake initially, but seems to have worked out in the end. Finn and Lady Rainicorn still share a close bond, despite the fact that Finn can't understand Lady Rainicorn without her universal translator.

Princess Bubblegum
Finn has a rather obvious crush on Princess Bubblegum, often having fantasies about her saying things like, "You're so cute, Finn!" or even kissing him. The best proof of this is in Business Time, when Finn does an imitation of Princess Bubblegum in a high-pitched voice, accidentally revealing that he thinks her voice is attractive. He often blushes at things she says to him, as in the episode Ricardio the Heart Guy when, as a joke, Princess Bubblegum asked Finn to kiss her. Finn also got extremely jealous of Ricardio, who was hanging out with Princess Bubblegum more than he was comfortable with. He got so envious that he came up to Princess Bubblegum and Ricardio and interrupted a scientific conversation between the two to ask if Princess Bubblegum wanted to hang out with him, all the while doing the Science Dance to impress her. Finn denies that he was ever jealous, however, constantly making excuses and even shouting, "I'm not jealous! I'm WEIRD!!!" There was also a chapter in the Enchiridion dedicated to kissing princesses, and Finn blushed as he read it. The princess calls him by his full name (Finn the Human) in the episode The Enchiridion, which shows some evidence that their relationship may be a little formal, although this has only happened once and most of the time they behave like very close friends.

Marceline
Finn's relationship with Marceline is clouded a bit by the fact that Marceline is a vampire. At the beginning of the episode Evicted, Finn seemed to have interest in Marceline, though perhaps not romantically like his relationship with Princess Bubblegum. Fascinated with her powers and abilities, he seemed to want to be friends with her until she kicked them out of their own home. In the music montage for Evicted, the singer refers to Marceline as a "sexy vampire lady", though it is unknown if Finn feels this way. Finn has been known to blush around Marceline, especially when she kissed his cheek. He soon gets over this embarrassment though, and seems to be frightened of her more than he is attracted to her. Finn and Marceline share a friend/enemy type relationship.

Quotes
See Finn/Quotes

Trivia

 * In the pilot episode/short Finn was named Pen, a name he got from the show's director and producer, Pendleton Ward.
 * In the pilot, Finn is voiced by Zack Shada. However, in the series, he is voiced by Zack's younger brother, Jeremy Shada.
 * Even though Finn can't swim in the episode Ocean of Fear, he was seen swimming in a lake in the episode Business Time and My Two Favorite People. This may only be because he has a specific fear of the ocean, and not small bodies of water such as lakes.
 * Jake says Finn cries whenever he poops. (Memories of Boom Boom Mountain)
 * Finn's hat has a small resemblance of Bueno the Bear from "Barrista" (a short from Pendleton Ward).
 * Finn is left-handed when writing or drawing, but uses his sword with his right hand. In Business Time, he used his sword with his left hand for a short period of time, and then switched back again.
 * His hat somewhat resembles the boy's hat from Where the Wild Things Are. Also, the two 'ears' on his hat are portrayed as a cat's ears in FusionFall.
 * Because it was never proven that Finn and Jake got their magical abilities (Wizard) taken away from them, both Finn and Jake still have their magical abilities. It is possible that the impact of the meteor that crashed into the Wizarding School could have taken away Finn and Jake's magical abilities. This, however, is unlikely, since all that appeared to happen to them after the meteor crashed was the spontaneous combustion of their clothes and fur. Finn's hat, however, remained intact, though with a few burn holes and scorch marks.
 * Finn and Jake can accurately tell what time it is by looking at how the sun affects the trees, stated by Pendleton Ward, the creator of Adventure Time.
 * In the Animated Short, the hole in his hat is half of a circle, instead of a full circle in the cartoon.
 * Finn has Thalassophobia, which is a fear of oceans or seas.
 * Finn is probably going through puberty, as in some episodes his voice cracks.
 * It is possible Finn's last name is Ward, as in When Wedding Bells Thaw, Ice King wonders if to himself if he is at the Ward household. On the other hand this could just be an inside joke within the staff, as Finn's original name was Pen Ward.