Wizard: Gaara is the son of the Fourth Kazekage, leader of the village hidden in the sand. Born prematurely at the cost of his mother's life, Gaara was destined for a childhood of depression and loneliness from the get-go.
Boomstick: Not even a minute old and already has a kill under his belt. Though, technically he had a little help. Because... You see... As he was being born, his father was like, "Hey, you know what would be awesome? Using ninja magic to seal a horrible monster in my son's belly to turn him into an ultimate weapon!"
Wizard: The process was successful and Gaara became a jinchuriki: human beings who have powerful tailed beasts trapped within them. Gaara's beast was Shukaku, a giant tanuki with power over sand.
Boomstick: Aww, I want a tanuki as a pet. They're so fluffy and adorable, you just wanna hug...
[sees Shukaku]
Boomstick: HOLY SHIT, WHAT IS THAT?
Wizard: Shukaku loathed humanity, and at first, Gaara had difficulties controlling the monster's rage, accidentally hurting others. As such, he was shunned by his own people, forced to live a secluded life.
Boomstick: Well, yeah, I mean, he's got a goddamn tummy monster. It's not like Pepto-Bismol's solving that.
Wizard: Convinced his only option was to fight and care for only himself, Gaara became a ruthless killing machine.
Boomstick: But it's not all bad. Having a digestive desert demon gives him control over all things sand.