Jake (full title: Jake the Dog Senior), the deuteragonist of Adventure Time, is a dog/shape-shifter hybrid, referred to by others as a "magical dog," and Finn The Human's companion, best friend, and adoptive brother. Jake has a unique set of abilities called Stretchy Powers that allow him to manipulate the shape and size of his body, coming in handy on innumerable occasions throughout his and Finn's adventures. Jake was 28 years old at his debut in "magical dog years," and ages throughout the series, though he rarely acts mature. It is inferred that magical dogs have a lifespan similar to Humans, as demonstrated by an aged Jake in "Dungeon Train." Then again, how exactly magical dog years correlate to human years remains to be seen, although both Finn and Jake were shown to be babies around the same time, showing that they age slightly faster, however, his age as of "Joshua and Margaret Investigations" suggests that it slows down to the rate of human's aging at some point. Jake is currently in a relationship with Lady Rainicorn, and, by "Jake the Dad," they are the parents of five Rainicorn-dog hybrids. Despite having impregnated Lady Rainicorn and helping her raise their 5 puppies: Charlie, T.V., Kim Kil Wan, Viola, and Jake Jr. Jake was never officially married to her. Even referring to her as his girlfriend and never his wife.

In "Skyhooks II", "Joshua and Margaret Investigations" and "Jake the Starchild" it is revealed that Jake's father is an alien shapeshifter named Warren Ampersand, who impregnated his dad Joshua. This hybrid heritage is the source of his shapeshifting/stretchy powers.

As of the New Adventure Time Miniseries' of Adventure Time: Distant Lands and Fionna & Cake, it is confirmed that Jake's aging is actually roughly equivalent to that of a non-magical dog. This means between the beginning of the series where Finn is 12 and Jake is 28 in Dog Years and Obsidian where Finn is in his Mid 20's, Jake would have been somewhere between 98 to 119 in dog years. At this current point in the series Jake the Dog has died of old age. Finn has tattooed Jake's face on his chest surrounded by forget-me-nots. Finn later convinces Jake to reincarnate with him.

Trivia:

• He is voiced by John DiMaggio.