Performer(s) Appeared in Jake the Dog is one of the main characters from the Cartoon Network original series Adventure Time. He is a magical shape-shifting dog who is Finn's adoptive brother and best friend. His magic powers allow him to stretch or shrink any part of his body to any shape and almost any size, ranging from becoming gigantic to becoming incredibly small. Acting as a confidant and mentor to Finn (though he has a tendency to give somewhat questionable advice), Jake has a laid-back attitude in most situations, but loves adventure and will eagerly fight when he needs to. His powers help Finn considerably in combat and transportation, but are also sometimes used as nothing more than jovial forms of expression.