Margaret

Margaret is a dog, the mother of Jake, Finn, and Jermaine. Natasha Allegri has confirmed that she and her husband Joshua adopted Finn as a baby. The couple first appeared in one of Finn's flashbacks in the episode "Memories of Boom Boom Mountain." They find Finn after he has soiled himself, causing him to be stuck to a leaf, and cried for an entire day, all alone in the forest. They are the first and only people to stop and help baby Finn, as all other passersby simply ignored him. They take him to what is presumably their house and raise him as their own. Margaret appears to be caring and loving. She speaks in a 1940s American accent.

According to Finn in "Conquest of Cuteness," Margaret always had "the right thing to say" whenever he or Jake were in a crisis. Strangely, a Two Headed Cutie tried to exploit their love for her during their invasion, pretending to be her ghost mocking them in an attempt to find their weaknesses.

In "Jake vs. Me-Mow," it is revealed that she had a special lullaby for Finn and Jake. Finn kept her music box in his backpack. It is assumed that he kept it as a memento of her.

Margaret, as well as her husband Joshua had passed away prior to the events of Adventure Time. The cause of death is unknown, but is assumed to be old age due to a normal dog's short lifespan.

Quotes
"Give it here, Joshua. This baby just needs some love and kisses to be happy."

Appearances

 * Memories of Boom Boom Mountain
 * Rainy Day Daydream (mentioned)
 * Conquest of Cuteness (mentioned)
 * Memory of a Memory (picture)
 * Jake vs. Me-Mow (mentioned)
 * Beautopia (mentioned)
 * Hug Wolf (mentioned)

Trivia

 * Margaret is confirmed to be deceased.
 * Unlike Jake, she could not stretch or expand, because she didn't have Jake's magical abilities.
 * In Rainy Day Daydream, Jake accidentally imagined his mother naked when his Imagination Machine was set to overdrive. However, Margaret "naked" (without her hat and earrings) would be an ordinary dog like Jake, but to him that could be a traumatic thing.
 * In Beautopia, Jake sees the largest and most grotesque of the Lub Glubs and says with awe, "That reminds me of my mother," for unknown reasons.
 * It is unknown how old Finn was when she died since he has many fond memories of her.