The Cosmic Owl is a mysterious creature known to the inhabitants of Ooo. He seems to have a country-like dialect.
The owl first appears in "Prisoners of Love" in Ice King's Imagination Zone, after Ice King is knocked out by Finn. When Ice King contemplates why people do not like him, the Cosmic Owl answers, "You're a sociopath."
The Cosmic Owl again appears in the episode "Donny" as a drawing made by the Why-Wolf. It is stated that the Why-Wolves, if not stopped, would ravage the world and overpopulate until the Cosmic Owl would be forced to intervene by devouring them all, as is the course of nature.
He appears in "The New Frontier" at the end of Jake's "croak dream," and Finn and Jake's later conversation suggests that it is well known that the Cosmic Owl is supposed to show up in croak dreams. The owl is also featured prominently on the episode's title card.
The Cosmic Owl also appears in "The Lich," where he is seen in Finn's dream on a television screen, indicating that Finn is in a "premonition dream."
He also appears in "Jake the Dog," visiting his friend Prismo in the Time Room inside the Multiverse while Jake is making his wish. At first, he is disappointed that he and Prismo could not play board games like they planned to, but he does join Jake and Prismo in the pool party.
In "Frost & Fire," the Cosmic Owl appears in Finn's dreams, foretelling his inevitable break-up with Flame Princess. Three times, Finn attempts to experience the "cool" and "important" dream again because the Cosmic Owl is there. Over the three dreams, the Cosmic Owl whispers something that Finn cannot hear, until the final premonition dream, where he stands directly in front of him. At this point, Flame Princess and Ice King are engaging in a full-out war. The Owl tells him knowingly, "You blew it." After Flame Princess breaks up with Finn, the premonition is realized, and Ice King repeats the Cosmic Owl's message to Finn: "You blew it, man."
The Cosmic Owl makes an appearance in "Wake Up," at Prismo's party. When Jake and Finn return to the Time Room, the Cosmic Owl is seen wanting to play another round of Card Wars with a disgruntled Prismo. He soon leaves after they beginning talking about the Citadel.