Jake

Jake is a magical dog in Adventure Time with Finn and Jake. Finn refers to him as his friend and will often get offended if others say that Jake is his dog. His known powers from the television series consist of: the ability to change in size and shape, as well as move his guts around, which repeatedly comes in handy in their adventures. He also likes to play a musical instrument called a viola.

Appearance
Jake is a light-orange dog with large eyes that characterize him greatly. His appearance can change many times since he has the ability to morph. His eyes are similar to Lady Rainicorn.

Personality
Jake is mainly laid-back. He often cracks jokes at serious times, but if Finn is feeling disheartened Jake always has a lecture or a song to cheer him up. He always has great advice when something bad happens, like in the episode Evicted, where he suggests house-hunting. He is afraid of Marceline because of all of the scary stories he has heard from, "reliable sources," made up or not. He believes he'll die if he eats chocolate or fudge, because a dog can't eat that kind of food. He can be somewhat irresponsible at times, frequently leaving Finn to fight most of a battle on his own, but he always pulls through in the end.

Rainicorn
Jake has a crush on Rainicorn and it has been stated on marketing material, although in the show it is only somewhat noticeable. On the official website in Rainicorn's description it says she is Jake's girlfriend and that they get along so well because of their common interest in the viola. At the beginning of Slumber Party Panic, he is shown playfully chasing Rainicorn, and later in the episode he doesn't seem to mind being locked in a closet for 7 minutes with her.

This relationship is also seen in My Two Favorite People. Also, it is shown in the same episode that he and Rainicorn are a couple.

Finn
Finn and Jake are best friends and will go out of each others way to protect each other. Jake watches over Finn using his stretchy powers to protect him, whether it is shielding him from rain or cold weather, or catching him in mid-fall. They're so close that Jake knows that Finn has a crush on Princess Bubblegum (though Jake probably found this out on his own, because Finn is terrible at hiding it). This relationship existed from the start of the series. They often do everything together (or try to, as shown in "My Two Favorite People").

Others
While Finn and Rainicorn are apparently Jake's two favorite people, he has a number of other acquaintances, listed in his cell phone as Doug, Todd, Jerry, Dennis, Reggie, Peter, George, Larry, Luke, David, Benton, Mike R, Mike H, Mike A, Gareth, Jennings (or possibly Garth Jennings,) Mr. International, Mr. Outrageous, Captain Majesty, The Flying Lettuce Brothers (FlyL.Bros), Pete The Punk (PeteT.Punk), and Tiffany.

Shelby, an earthworm and friend of Jake, lives in his viola.

In Memories of Boom Boom Mountain, Joshua, a dog who resembles Jake (but wearing a grey fedora) and Margaret, another dog who resembles Jake (but wearing earrings and a peach hat) find the infant Finn. It is not known however, if they are related to Jake himself. It is noteworthy that both Finn and Jake call each other "brother" in the same episode. Whether it is coincidence or an implication that Jake is Finn's adoptive brother is unclear as of yet.

There is also a dolphin who has fallen in love with Jake, which Finn considers to be a boon.

Quotes
See Jake/Quotes

Trivia

 * Jake shares the same voice actor with Shnitzel from Chowder, Bender from Futurama, Rath from Ben 10: Alien Force and Ben 10: Ultimate Alien, and Rico from Penguins of Madagascar.
 * Jake has at least 22 contacts on his phone, possibly more.
 * Because it was never proven that Finn and Jake got their magical abilities (Wizard) taken away from them, both Finn and Jake still have magical powers. (Jake's favorite power is one that allows him to sleep on command, though Finn found that one uninteresting.)
 * Finn and Jake can accurately tell what time it is by looking at how the sun affects the trees, stated by Pendleton Ward, the creator of Adventure Time.