An outcast mist nin and Zabuza's assistant. He was a young child living with his parents in the mist village, living happily with both. It wasn't long after that until he discovered he had an advanced bloodline, however, and had the ability to manipulate ice. He inherited it from his mother, and when his father discovered it, he killed her, and tried to kill Haku. Haku killed his father rather, and then was abandoned. Zabuza found him later, and forced him to learn his combat abilities.
In Zabuza's second fight with Kakashi, Haku got between the two and sacrificed himself, becoming impaled by Kakashi's chidori
. This was how Haku died.
Haku is very fast. He wears the mask of a hunter-nin, and was trained as one, although I believe he's an unofficial ninja (meaning he doesn't apply to the genin/chuunin/jounin ranking system). When fighting, Haku's seemingly ruthless, but he's actually pure-hearted.He's very pretty, too!