Sakumo Hatake

, also known as, is the father of Kakashi Hatake. Sakumo was the enemy of Chiyo's son and his wife. Based on implication, it is most likely that he killed them during the war.

Personality
He was deeply devoted to his country and put his friends and teammates before anything else, even at the cost of a very important mission.

Kakashi Gaiden
According to the Fourth Hokage, Sakumo was once respected as much as the Sannin before he fell into disgrace after botching a mission that caused Konohagakure to suffer great losses. Despite knowing how critically important completion of the mission was, Sakumo had chosen to save the lives of his comrades over the success of the mission. He failed the mission and was discredited by the Leaf Village and even the people he rescued.. Dishonored, Sakumo committed suicide after deep depression and a drop in his skills, which caused Kakashi to lead his life strictly according to the Ninja code. Sakumo left his, for which he was nicknamed, to Kakashi, which utilized chakra to produce a trail of white light from the blade when swung (the blade being the metaphorical "fang"). It was cut in half during a fight between Kakashi and an Iwagakure shinobi.

Rescue Gaara Arc
When Kakashi and his team arrive in Sunagakure, he is instantly attacked by Chiyo who mistakes him for his father. It is implied that Sakumo once killed Chiyo's son and his wife, during the war with the country.

Pain Invasion Arc
During the battle against Pain, as Kakashi feels himself losing strength and consciousness, Kakashi finds himself in an area of darkness, where Sakumo meets up with his son to talk.