The Demon Cat is a minor villain in Adventure Time.
He is voiced by Clancy Brown, who also played Hades in the God of War videogames, Mr. Krabs in the SpongeBob SquarePants franchise, Undertow in Disney's The Little Mermaid II: Return to the Sea, Savage Opress in Star Wars: The Clone Wars, Silas in Transformers Prime, General McGuffin in Wander Over Yonder, General Wade Eiling in The Flash, Viking Lofgren in Bad Boys, Surtur in Thor: Ragnarok, Gunmar in Trollhunters, Harry Bordon in Cast a Deadly Spell, Parallax in Green Lantern, and Lex Luthor in the DC Animated Universe.
The Demon Cat is a large teal cat-like creature, with razor sharp teeth and retractable claws. He has yellow-green eyes with pinkish-red pupils. He has a pair of very short teal-colored ears, resembling that of a cat. Small sections of his right foreleg and hind leg are invisible (or non-existent), and his tail seems to be made of maroon tentacles that extend from his body. He has small magenta bumps that come out various places on his back and chest as well. The Demon Cat can create a lure from his mouth that resembles the head of a kitten. He can also turn his kitten tongue upside-down.
The Demon Cat seems to take great pride in his "approximate knowledge of many things," meaning that he "kind of knows things." Examples include almost knowing Finn's name (calling him Frank), And later calling him Jim, knowing where Finn "might" be hiding, and referring to Jake as "Jack." The Demon Cat also seems to enjoy toying with and tormenting his victims, announcing his intentions, movements, and plans to Finn while searching for him. The Demon Cat speaks with a creepy yet calm voice. His eyes also turn red, possibly due to them swelling up with blood, when he gets angry. It is somewhat unclear if he hunts for food, pleasure, or as a guardian in the dungeon. He claims throughout the episode that he will eat Finn's eyes, skin him, and tear out his heart (among other things). He has a very sadistic personality. The Demon Cat is unafraid of adventurers such as Finn, but is terrified of dogs, running away from the mere smell of Jake.
The Demon Cat is first encountered by Finn near the beginning of the dungeon, where he engages Finn in combat. Finn punches him in the face, enraging him and causing the yellow sclerae in his eyes to turn blood red. He easily beats Finn in single combat, only to suddenly retreat when he notices Jake's odor on Finn. After escaping the Bucket Knight, Finn lands in the Demon Cat's lair. Awaking to Finn complaining that Jake is not accompanying him, the Demon Cat decides to resume his attack. Finn is forced to flee from the Demon Cat and hides in a nearby cavern. Using his knowledge of "exactly where Finn might be," the Demon Cat begins searching for Finn. Fortunately for Finn, the Demon Cat's approximate knowledge is unable to pinpoint his exact location; although, with the limited number of hiding spaces within the cavern, Finn seems doomed. Only through the arrival of his "Guardian Angel" is Finn saved from the Demon Cat.
- It is likely that the Demon Cat is a parody or tribute to the Displacer Beast, a monster in Dungeons & Dragons that looks like a puma with tentacles coming out of its back and makes illusions of itself to confuse others. In this case, the Demon Cat is often misplacing others or information.
- The Demon Cat's tongue may be a parody of the Xenomorph's tongue in the Alien movies. When he first appears, it is shown that his tongue is a small kitten.
- The Demon Cat is the boss in the game Sound Castle.
- He claims the Crystal Eye Dungeon to be "his" dungeon.
- Demon Cat appears in Cover 16B, featured under Cover Art in the Adventure Time Comics vol. 4.
- This character may also be a subtle reference to Schrödinger's Cat. For example, he knows "exactly where Finn might be." Also, parts of his body appear nonexistent.
- He appears as the first boss in the game Adventure Time: Explore the Dungeon Because I DON’T KNOW!.
- The Demon Cat's voice sounds similar to that of famous horror star Vincent Price.
- The Demon Cat is a boss in the first dungeon in the game Royal Ruckus.
- In Gears of War 4 there is an achievement named "I Have Approximate Knowledge of Many Things" which is most likely a reference to the Demon Cat.