Haku

Haku is a ninja from the Land of Water, who has the ability to control two types of nature chakra (most can only control one): water and wind chakra. This gives Haku the ability to use ice chakra which is a mixture of the two. Haku's ability to use ice is the result of Haku's kekkei genkai known as Hyoton, which is literally translated as "Ice Release" in English.

History
Haku was born near a snowy village in the Land of Water, a land that had suffered from war not long before. In this war, different sides battled each other using ninja, some of whom possessed kekkei genkai, which are passed down through the generations. After the war ended, memories of the horrific battles still lingered in the minds of the people. Those with kekkei genkai quickly became feared and hated for their ability out of concern that their existence would only bring about more war.

Haku's father and mother were simple farmers, but they lived a peaceful life. They loved each other and were kind to their child. Unfortunately, this all changed one day. The mother was a carrier of a kekkei genkai. She hid this fact from her husband, hoping that the love and peace that was shared in their small family would last forever. One day, Haku discovered the ability to manipulate water. Amazed by this, Haku proudly showed this to the mother, who was horrified by what she saw and harshly scolded Haku for displaying the kekkei genkai's ability. After a slap to Haku's face and a few harsh words, the mother embraced her child and apologized.

Unknown to the mother, Haku's father had seen everything. When Haku's father discovered that his wife and child possessed a kekkei genkai, that evening he assembled a small mob of villagers and killed his wife. He would have done the same to Haku, but before he could, Haku killed him and the others out of reflex using the advanced bloodline's ability to create ice shards.

Haku had become an orphan who was wanted by no one. Haku was forced to take to the cold streets and rummage through trash bins for scraps of food, even sometimes having to fight off the wild mongrel dogs that roamed the same streets and ate the same scraps of food.

Arc 2: Mission to the Land of Waves
Some time after this Haku met Zabuza Momochi, a missing-nin, and joined him with the vow to become his "weapon", which meant to become Zabuza's shinobi. Zabuza took Haku in, and gave Haku's life meaning and purpose. He also trained Haku in the ways of shinobi, as well as every fighting technique that he knew. During Team 7's mission to the Land of Waves, Haku appears as a hunter-nin, giving the impression of being sent to kill Zabuza (when in reality was there to save him). Haku was soon revealed to be Zabuza's subordinate in the story and fought Sasuke and Naruto on the Great Naruto Bridge.

Haku fought for and protected Zabuza. Haku's dream was to make Zabuza's dream of ruling over the Land of Water come true. This was Haku's purpose in life before Naruto defeated Haku and took that purpose away. Haku, no longer having a purpose in life or being of any use to Zabuza as a weapon, wished for death. But before Naruto could deal the finishing blow as requested, Haku used the Demonic Ice Mirrors and throwing needles to release Zabuza from Kakashi's summoning as well as to take the full force of his Lightning Blade. Haku's noble and selfless sacrifice for the one who mattered most allowed Zabuza to avoid certain death. Despite Haku's efforts, Zabuza was eventually defeated by Kakashi and then killed by the combined efforts of Gatou's hired thugs.

Other involvement
In the anime, it is revealed that Haku and Zabuza met Kimimaro some time after Zabuza cast aside the Land of Water and set out with Haku, but the manga does not present this meeting.