Jake

Jake is a magical dog in Adventure Time. 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 is the son of Joshua and Margaret. Jake is 28 years old (4 years old in human years), but sometimes he acts less mature. He also likes to play the viola.

Appearance
Jake is a golden-colored bulldog with large, characteristic eyes. His appearance can change drastically due to his ability to morph. His fur compliments his viola.

Abilities
Jake has the ability to shape-shift, meaning he can control the size, shape, and dimensions of his body. Not only can he stretch and contort himself, and form recognizable shapes from parts of his body, but he can also rearrange his internal organs. One common use of his powers is Key Hand, which he uses to open locks. He also has a supernatural sense of smell, as he can apparently smell the specific location of objects from miles and miles away. He also owns a sword and an axe, but he never uses them for combat. Apparently, anything he imagines becomes real, but only visible to himself. He can also play the viola, which can have peculiar powers if certain artists are played, such as summoning snakes when he plays a piece by Mozart.

Personality
Jake is generally laid-back and usually does not worry about things. 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 is always willing to give input and advice about a situation, but his suggestions are usually inconsistent; they range from encouraging a helpful, fresh perspective to ridiculous nonsense. He can be somewhat irresponsible at times, frequently leaving Finn to fight most of a battle on his own, but he always pulls through when he is needed most. He's very conscious about his viola.

Lady Rainicorn
Rainicorn is Jake's girlfriend. 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.

It is shown that Jake can speak, understand, and decipher what Rainicorn says. A loyal boyfriend, Jake often leaves adventuring for a while to make time for Lady Rainicorn.

Finn
Finn and Jake are best friends and will go out of their 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. Jake is fully aware of Finn's crush on Princess Bubblegum (though Finn still denies it) and even helps him try to win her over. Having been raised together by Jake's parents, the two share a brotherly relationship. Jake often acts as a force of guidance in Finn's life, giving out whatever advice he sees best. Though they have seemingly contrasting personalities, Finn's manic hyperactivity and Jake's genuinely lazy demeanor, the pair make an excellent team and are immensely important figures in each other's lives.

Tree Trunks
Jake and Tree Trunks share a close relationship, which is similar to a grandmother-grandson relationship. This is shown most of the time, though there was a situation in the episode "Tree Trunks" when she kissed him several times so that he would let her help Finn. Jake appeared later with lipstick marks all over his face, and he was smiling. Later, Tree Trunks tells Finn that she'll accept his apology (Finn had earlier yelled at her) if he would let her kiss his cheek. Finn was about to decline the offer when Jake says "Whoa, let her kiss your cheek, man! It's a once-in-a-lifetime opportunity!" Other than this, there are no evidences of a romantic relationship between Jake and Tree Trunks, although they remain close friends.

Marceline
Jake has a fear of vampires, which makes him terrified of Marceline. Marceline cannot help it and likes to scare Jake, but in "Henchman," Jake will not accept the fact that Marceline is not evil, and almost murders her by exposing her to sunlight.

Princess Bubblegum
Jake is very aware of Finn's crush on Princess Bubblegum, so Princess Bubblegum and Jake have a rather strange relationship.

Others
While Finn and Rainicorn are apparently Jake's two favorite people, he has a number of other acquaintances, listed in his cell phone (see Jake's Phone).

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. They were in fact, confirmed to be Jake's parents in the Adventure Time Frederator Blog. (See Joshua And Margaret).

Jake and the Squirrel are enemies, because Jake wouldn't publish the Squirrel's letter in his newspaper advice column, and now the Squirrel wants revenge.

Quotes
See Jake/Quotes.

Trivia

 * Jake's voice actor is John DiMaggio who has also voiced with Marcus Fenix in Gears of War 1 and 2, various Brutes in Halo 3 and Halo 3 ODST, Shnitzel from Chowder, Bender from Futurama, Rath from Ben 10: Alien Force and Ben 10: Ultimate Alien, Jocktopus from Fish Hooks, Rico from Penguins of Madagascar, and Bobo from Generator Rex.
 * Jake has at least 23 contacts on his phone.
 * Finn and Jake can accurately tell what time it is by looking at how the sun affects the trees.
 * Confirmed on http://www.formspring.me/buenothebear, Finn and Jake's parents (presumably Joshua and Margaret) are dead.
 * In "The Witch's Garden", Jake tried to remember how he got his powers, and came up with the idea that he got his powers by rolling in a mud puddle.
 * When Pendleton Ward was asked on his formspring if the mud puddle that Jake rolled in as a pup was really where he got his powers, Pen stated that it wasn't, and that Jake just couldn't remember.
 * Jake writes a newspaper column titled "Begs the Question."
 * Jake wears invisible pants spun from spider webs by pixies, as seen in the episode "Donny".
 * It was implied in the episode "Freak City" that Jake has a foot fetish.
 * He does a parody of "Double Rainbow".
 * Jake was confirmed to be a bulldog on Pen's Formspring.
 * Jake seems to have Sanguivoriphobia (fear of vampires).
 * Jake has a tendency to steal items without realizing what he is doing, as seen in "The Witch's Garden" and "City of Thieves".
 * Jake thinks he is hot, yet hates when he is called cute. This may suggest that he has a narcissistic attitude.
 * Jake, while being magical and somewhat intelligent, does retain some tendencies of a dog including:
 * Rolling in the mud ("The Witch's Garden")
 * Chasing strange objects ("Dungeon")
 * Sniffing poop ("Gut Grinder")
 * A love of belly rubs ("Gut Grinder")
 * Jake can be stretched by force as seen in "Ocean of Fear," where Finn stretched Jake's ears to avoid making contact with the ocean.
 * Jake is assumed to be the only dog in Ooo, because when asked on his formspring if there were any other dogs in Ooo, Pen said, "There's wolves".
 * During his flashback as a child in the episode "Crystals Have Power", Jake was shown to have a brother, named Jermaine.