Hokarou Hyuga is the father of Seireitou Hyuga and a former member of the Hyuga clan of Konohagakure. He met a girl named Kikyo from another clan who he fell in love with and married her. However the Hyuga clan forbid such a marrige, because they did not want a member of their clan marrying with someone outside of their clan. When they married, the Hyuga elders had removed Hokarou from the clan. Soon after, villagers of Konoha begin to grow angry and attacked both Hokarou and his wife. Danzo, who also grew angry of this, ordered all of Anbu Root to murder both Hokarou and his wife. They attack them and kill the two of them. This was just after a day since Seireitou was born, and the villagers attemped to kill him too, but the Third Hokage and Minato stopped their assult and told them to leave at once. The third then took Seireitou and left in Minato Namikaze's care (this was about 5 years before minato met kushina uzumaki) until seireitou become 4 years old and he was put into the ninja academy. Seireitou was never told that Minato was caring for him after a jutsu wiped his mind clear of that. Seireitou was knocked out by the jutsu and put into a home that was given to him by the third hokage, which was stocked with money, food, water, and clothing. Seireitou thus began his life by himself, never knowing his parents or really anything from his childhood before 4 years old.
Not much was ever known about Hokarou's powers, but it is speculated that he was at Sannin-level, this being shown when Danzo had ordered all of Anbu Root to kill Hokarou, because he knew of Hokarou's great strength.