Jake is the adoptive brother and best friend of Finn. He's 28 (in "magical" dog years) and has the ability to shape-shift, stretch, grow and shrink to almost any size. He can also rearrange his internal organs, as well as his teeth. Jake acts as a confidant and mentor to Finn, although he sometimes offers questionable advice.
Jake has a laid-back attitude and can be considered lazy at times. He relies on either his magical powers or Finn to rescue him from a dangerous predicaments. He can be seen as a form of comic relief, cracking jokes in tense scenes and always knows how to cheer Finn up when he's feeling disheartened or troubled. Jake also acts as Finn's "world-wise mentor", always willing to give his input and advice on a given situation. However, his suggestions are often inconsistent and can be confusing, ranging from helpful encouragement and quirky ideas, to ridiculous nonsense. Furthermore, he can be considered somewhat irresponsible at times, leaving Finn in peril to fight most of a battle himself, although he can always pull through and appears when Finn needs him most.
- He is in a relationship with Lady Rainicorn and they have five dog-rainicorn hybrid pups in a future episode.
- He is quite skilled at playing the Viola
- He can shrink and move his internal organs and blood into his left thumb
- Jake can move objects through his body freely (in and episode, PB jumps into Jake's mouth and is pushed out of his back)
- It is apparent that Jake uses his powers lazily and cannot know their full extent
- Jake claims to have obtained his powers while rolling in a magical mud puddle as a pup...but the show's creator reveals in an interview that this is not the actual source of his power...he just can't remember
- He also has an older brother named Jerome
- While growing up, Jake found time to escape and land himself in trouble leading a double life as a criminal with a gang of bad friends
- He may be dyslexic (he is seen writing backwards), although Finn also writes backwards and it may be because of their upbringing, or possibly a commonality in the Land of Ooo
- He loves to eat - especially junk food!
- Jake possesses symptoms of ADD; he can forget a conversation in a moment, distracted by the need to do something completely unrelated, such as putting an ice cream cone in the toaster, and has difficulty focussing on anything
- He's seen to have somewhat of a dark side through certain episodes, making questionable comments which might appear evil or selfish (evidenced when he wants to rule and control the "Hyoomans", a tribe of human-like creatures with fish gills who live underground, and when he mentions that he used to "[steal] old ladies' purses" and "hock stolen bikes")
When Jake shape-shifted into a demon to blend in when both him and Finn were in the Nightosphere