Yagami, Souichirou

Soichiro Yagami is Light's father and detective superintendent of Japan's National Police Agency. He initially leads the Kira investigation team that later joins with L. When L begins to suspect Light of being Kira, Soichiro is unwilling to believe his son would be capable of such a thing.

[Spoiler] After Light and Misa Amane are held in surveillance by L for over 50 days, Soichiro was told to play a stunt where he tries to kill Light and then himself out of guilt. After seeing Light and Misa's reaction, they get out of suspicion by L. [/Spoiler]

[Spoiler] After L's death, he is sent to retrieve the Death Note stolen by Mello, though Light had planned for Matsuda to fill the role. He retrieves the Note and learns Mello's real name, but is unable to kill him and is instead fatally wounded. Because Light has given up his Death Note, making his lifespan visible above his head, Soichiro dies believing that Light is not Kira. [/Spoiler]

(Source: Wikipedia, edited)