Hizashi Hyūga

was a member of the Hyūga Clan. He was the father of Neji Hyūga, the younger twin brother of Hiashi Hyūga, and the paternal uncle of Hinata and Hanabi Hyūga.

Background
Hizashi Hyūga was Hiashi Hyūga's twin brother, but, as he was born seconds later, Hiashi was made the successor to the clan, whereas Hizashi was made a member of a branch house. At some point in Hizashi's life, he was branded with a curse mark that could be used to punish him if he disobeyed the main branch, and would seal the Byakugan when he died.

He eventually fathered a son, Neji. On Hinata's third birthday, Hiashi branded Neji with a curse mark. At this time, Hizashi was aware of Neji's talent, and began to resent that Neji would be forced to serve the main household. As such, he gave Hinata a glare filled with murderous intent, in which Hiashi responded by activating the cursed seal, causing Hizashi intense pain as punishment.

Death and Legacy
After Hiashi killed the Head Ninja of Kumogakure to save Hinata, Kumogakure demanded his body, claiming to want it as restitution - in reality, they wanted to obtain the secrets of the Byakugan. At this point, the clan elders proposed sending Hizashi's body in Hiashi's place, ensuring that the Byakugan's secret would not be discovered.

While Hiashi refused, and insisted on offering himself instead, he learned that Hizashi had already agreed. Hizashi disabled Hiashi with a single blow when he tried to stop him. He then calmly stated that, while he still hated the head family, he chose death to save his brother, to prevent war, and to decide his own destiny. He asked Hiashi to tell Neji of his reason for his decision, regretting that he had shown Neji his bitterness in life. Hiashi chose not to tell Neji until he believed he was mentally ready, and Hizashi's death led to Neji's blaming the main house and believing that fate couldn't be changed. Neji eventually learned the truth after being defeated by Naruto in the finals of the Chūnin Exams, and, in the anime, read his father's final letter. Upon realizing this, Neji forgave the main family, and silently told his father of his new dream to never lose again.

The affair surrounding Hizashi's death is quite well-known among the high-ranking ninja of Konoha, most of them taking it as a serious infraction of Kumogakure. This was shown when Yamato called out the Fourth Raikage for his relentless pursuit of Sasuke Uchiha, comparing the latter's theft of Killer Bee to their attempted theft of the Byakugan and noting that Konohagakure remained magnanimous while they were vindictive.

Trivia

 * In English dub, the English voice actor for Hizashi also does the voice for his twin brother, Hiashi.