In " Together Again", Elderly Finn appears as an old man with a long, white beard and wrinkly skin. According to Adam Muto, Finn was confirmed to be fifteen years old in the second half of Season Five. A crudely-drawn version of Finn was seen in the Battle for Dream Island episode "Don't Pierce My Flesh" as a recommended character.

Despite being mischievous from time to time, Finn is a very kind-hearted person. It's shown multiple times that he shows clear concern for others, even for those who have willingly hurt him, such as in " The Enchiridion," he returned the dollar to the giant (note that this was the very same giant who ate his beloved brother Jake and even kept insisting that he was dead). Furthermore, he shows clear contempt for anything that is done out of immoral reasons and a consistent drive for righteousness—to "do the right thing." Finn's weight seems to fluctuate between episodes, with him seeming chubbier in some instances than others. Pendleton Ward stated on the "In Your Footsteps" commentary on the Season 4 DVD that his weight depends on how active he is adventuring, along with his diet, so it changes frequently. Finn also shows up in Adventure Time: Hey Ice King, Why'd You Steal Our Garbage?!! not only as the main character but, in the 3DS version, imputing the Konami code that shows an 8-bit version of Finn and Jake dancing with Pendleton Ward while he sings the secret song.

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This contradicts with " Min and Marty," where he is revealed to already have the name 'Finn' before being separated from his parents. In the same episode, it is shown that when Finn drifts alone in the raft, there is also a stuffed bear having his name tag on it along with him. At the beginning of the series, Finn's voice is more high pitched, but later near the latest episodes, Finn's voice is a bit deeper from puberty.

In the Adventure Time: Distant Lands special " Obsidian", an older Finn appears. His hair has darkened and is now a darker dirty blonde colour rather than the golden-yellow blonde from when he was younger. In " Preboot" it is revealed by the "human plus" Dr. Gross that are more humans outside of Ooo. This is further explained in the miniseries Islands, where it is revealed that roughly a thousand years prior to the main events of the series, a group of surviving humans from the Mushroom War fled Ooo on a container ship (as seen in Stakes) to escape from the vampires, oozers, and a comet. They eventually settled on a secluded island chain far from the mainland. Over the next thousand years, their community thrived and developed into an advanced technological society. While it was a veritable utopia, there were those few who occasionally grew dissatisfied with their rigidly structured lives and attempted to flee the island; these "hiders" were, in turn, hunted down and returned by specially trained "seekers." Finn, Jake, Susan Strong, and BMO went to the islands so that Finn could find out about his past and his species. In the app Lil' Alchemist by Kongregate, there is a card in the Huntress event that looks like Finn but has different colored clothes and skin. This character is called "Adventure Kid." Finn is shown to have an unrequited love for Princess Bubblegum throughout much of the series. He and Jake frequently have to rescue Princess Bubblegum from the obsessive Ice King. Finn's past life as Shoko, an orphaned thief who befriends and then betrays Princess Bubblegum, influences his present-day infatuation with Bubblegum. Finn's friendship with Bubblegum becomes more distant as the series progresses.Finn and Jake appeared four times on the series MAD. See References in other media for a detailed description. Aside from his normal outfit, Finn can be seen wearing a cream-yellow sweater in colder areas such as the Ice Kingdom but would wear his pink sweater made by Princess Bubblegum occasionally. In " Holly Jolly Secrets Part II," he wears a dark blue sweater with Christmas decorations on it and a green scarf. Finn also wears white briefs that make their first appearance in " City of Thieves" when Penny steals his shorts at the end of the episode. In " Who Would Win," he was shown to wear a different pair with red elastic. Finn sleeps in red footie pajamas that appear in many episodes, but in the animated short, he sleeps in a red sleeping bag in his regular clothes. In the series, the sleeping bag is beige. Little Dude's ability to possess people and be the host is similar to DC Comics supervillain, Starro. Also similar are the symbiotes Venom and Carnage from Marvel Comics. Finn states that Jake is "getting fat," even though in " Business Time," Jake can change his weight by using his Stretchy Powers. Though Finn may only be joking when he said this to Jake.

Tyr the One-Handed is the Norse god of war, sometimes equated with Mars. He lost his hand to Fenrir, the great wolf sired by Loki. Like most of the main characters, Finn is an Exosuit in the game Project Exonaut. His suit is in the "Banzai Squadron" (red) faction. After The Ancient Sleeping Magi of Life Giving mommy-magics Finn's red pajamas to life and they come of his body, Finn remains in nothing but his own underwear throughout the rest of the episode. Finn, Jake, Princess Bubblegum, Lady Rainicorn, Ice King, Stanley the watermelon, and the Reaper are characters in the game FusionFall, in which the player helps Finn save two princesses, get shirts from Stanley, and train with Finn in the petting zoo (Generator Rex). Besides combat, Finn displays many other impressive abilities in handicrafts. He has some origami skills, as shown in " Ricardio the Heart Guy," in which he makes Princess Bubblegum a paper crane, as well as in " Marceline's Closet," in which he makes a paper airplane. In addition to that Finn can also draw as seen in " The Thin Yellow Line" which he states that he isn't very good at it, as well as in " Mysterious Island" where he draws BMO and Susan. He is shown to be able to construct a sculpture of the Candy Kingdom from his saliva for Princess Bubblegum in " The Real You." Finn is also somewhat gifted at constructing simple machines, such as the catapult in " The Witch's Garden."

Finn's story arc as the last remaining human — and his eventual discovery of other humans — has been praised by critics. Zach Blumenfeld of Paste contrasted Finn's rootless and heroic existence to the passionless, technology-dependent lives of the other human survivors in Islands. Blumenfeld considered Finn to be an example of Friedrich Nietzsche's hypothetical Übermensch. Finn and Jake frequently use math terms as catch-phrases and at times censors for curse words. However, they are shown to be terrible at math, as confirmed in the episode " Slumber Party Panic." (Examples of these words include: mathematical, rhombus, algebraic and math). This was utilized less frequently as the show progressed, though it still occassionally appeared. A child in a Finn costume appeared in the Halloween episode of South Park "Nightmare on Face Time." In an interview in early 2012 (at the end of Season Three), Pendleton Ward stated that Finn was fourteen.

By the time period of " Together Again", many decades after the main series, Finn has become an elderly man with a long white beard. At this age, Finn dies presumably of old age, and he transcends into the 37th Dead World. In Issue 9, it is revealed that Finn had been called "Pen" in the original short because of his love for pens. Although originally, he was most likely named after the creator of Adventure Time, Pendleton Ward. A future Finn then takes his red sleeping bag when he and Jake leave to help Lady Rainicorn, also leaving a note of advice telling Finn to use his real name. This, however, is most likely non-canon. Finn] affirms life as it happens (both the good and the bad), constantly creates a value system and exists completely unfettered by society or the past. [...] He's grown up without the weight of human history and custom, has guided his own way through a flood of adolescent emotions and has become a hero in a dangerous land of his own free will. His moral code, once crafted in the image of his idol, Billy, is now of his own making. Finn is technically still the King of the Goblins; the goblins believe his scapegoat, Whisper Dan, to be him.In " Conquest of Cuteness," Finn was shown to have a crossbow. He uses a different one in " The New Frontier," although it appears he is less proficient with it than with a sword. Like other Adventure Time characters, Finn is drawn with rubbery "limp noodle" limbs and a simple but expressive face. He has several missing teeth, which Ward explained as being due to the character never having been to a dentist. He typically wears a signature white bear hat, and form-fitting clothing. Finn's visual design resembles Bueno the Bear, another character created by Ward. Finn and Bueno share some other similarities, including an enjoyment of beatboxing.