Key-per, or Gate Key-per, makes his first appearance in Adventure Time in the episode "The Enchiridion!" His key-shaped hat is, in fact, the key that opens the gate to Mount Cragdor. (This means that the Key-per himself must be literally inserted into the lock). After Finn uses him to open the gate, the Key-per asks how Finn figured it out. Finn replies, "I just thought you'd look cute stuffed in that lock." The Key-per affirms Finn's choice, saying this is the answer to the riddle. He also says that this is the same conclusion that previous adventurers reached to enter, but Finn and Jake are already leaving him behind.
Key-per is able to talk very fast, as is Booko in "The Lich," and his speeches are usually difficult to understand because of how quickly he says the words. He is the gate keeper to the pathway of The Enchiridion. After defeating the Dark Magician, Finn, in his rage, sees Key-per in red, devilish pajamas, mistakes him for another trial, and punches him in the stomach. The Key-per, lying hurt on the ground innocently, explains that they are his pajamas. He then makes spaghetti for the picnic after the quest along with Mannish Man, Finn, Jake, and a couple Old Ladies.
The Key-per is short and tubby, has yellow skin, and wears a baby-blue robe. He has tiny arms and chubby cheeks, and he appears to be missing teeth. He has round black dots for eyes, and unlike most other characters, he has visible slits for nostrils. He wears a key-shaped necklace on a chain, and a blue-grey hemispherical hat adorned with a large key in the shape of a backwards F (resembling an old skeleton key). His hat has a strap with a brown buckle, and appears to tightly squeeze his face.
Greetings, young heroes-to-be! This mountain is called Cragdor. Its purpose is two-fold: to protect the Enchiridion and to test the hearts of those who seek to possess it!
Many noble challengers have entered attempting to pass the grueling trials that lie behind these walls, but no one has ever left here alive or dead!
Oof! These are my pajamas! I was getting ready for bed.
- His name is a pun and a portmanteau of the words "key" and "keeper."
- Key-per is voiced by John Moschitta, Jr., who previously held the world record for the world's fastest talker. Moschitta is also known for voicing Blurr from another Cartoon Network Studios series Transformers Animated and the original Transformers series.
- In the game Righteous Quest, Key-per shows up twice: once in a red robe, and once in his original blue robe.
- The Key-per also appears in the second level of the game and the Ice Kingdom.
- The Key-per bears a strong resemblance to the Door Lord and Booko.
- The color and shape of his one-piece pajamas strongly resemble a stereotypical demon. Finn mistakes him for a threat because of it.
- It seems that Booko is the same species as Key-per.
- Key-per looks more feminine and much older in his concept art.
- It is possible that the Key-per is a miniature variant or subspecies of Door Lord, considering their similarities to that character in function, power, color, and facial features. However, they serve opposite purposes: one unlocks existing doors, and the other creates them.
- Also, the Key-per is small and wears robes and a key hat. The Door Lord is tall and wears nothing but a door hat.