Booko is a character from the Adventure Time episode "The Lich." He appears as a hologram through the Enchiridion, where he explains the functionality of the book's power and its link to the multiverse dimensions. He is accessed by the Lich, disguised as Billy, who beams a light from the gem over Billy's nose to the corner of the books shield graphic, which was a tiny compartment that revealed Booko. He is a very talkative person, and his speaking speed is fast but followable to those listening.
He appears as one of the toys in "All the Little People."
His appearance resembles the Key-per from "The Enchiridion!" and the Door Lord from "What Was Missing." He is tubby and wears a robe and a book-shaped hat. Since he is presented as a hologram to the viewers, his coloring is red.
In "All the Little People," his color scheme was revealed to be the same as Key-per's.
Hello, my name is Booko! What you see here is a map of the multiverse! It shows all the known dimensions and the links between each of them. This is the dimension that contains the universe in which we currently reside. At the center of the multiverse is a dimension called the Time Room, believed to be the quasi-corporeal dwelling place of the almighty Prismo. The Time Room is the single dimension that exists outside of time. The Time Room produces time waves that are experienced by other dimensions. Some dimensions have permanent links that allow travel to and fro. Others become linked temporarily by naturally forming Worm Holes. And others can become linked artificially by magical portals, torn open by items of great power. Once the last gem is inserted into the Enchiridion it will have the power to create a portal to any dimension in the multiverse. An activated portal creates a time dilation in which either end of the portal experiences a temporal synchronization allowing for the safe passage of particles through a non-local region of spacetime.