Risei Kotomine

Kotomine Risei is the father of Kotomine Kirei, the recurrent antagonist of Fate/stay night.

History
Kotomine Kirei's 80 year old father, Risei is a priest in the Church and the regulator of the third and fourth Holy Grail Wars. A friend of Tohsaka Tokiomi's, Risei actively supports him and conspires to ensure that Tokiomi will obtain the Holy Grail in the war, despite the fact that as a member of the Church, he should be ensuring only someone who is worthy of the a powerful artifact like the Grail should be obtaining it.

While he is proud of his son, who has demonstrated himself to be a perfect heir, Risei fails to understand Kirei in any sense. He believes that his son, who has recently lost his wife of two years, may be able to find some purpose in life again by aiding Tokiomi during the Holy Grail War.

Role
Both Risei and Tokiomi, upon discovering that Kirei's command mantra had appeared three years before the start of the war, both came to believe that Kirei was destined to provide Tokiomi with an additional Servant and associated command spells for the upcoming war. Without informing Kirei as to the true nature of the mark that appeared, they transfer Kirei from the Church to the Mages Association as Tokiomi's pupil. Neither man reveals to Kirei that he can also obtain the Holy Grail, instead telling the young man that he is performing a mission for the Church.

As Risei conspires with Tokiomi, they eventually come to see that Caster and his Master prove to be too erratic and threaten Tokiomi's chances of winning the war. To this end, they arrange for Risei to offer additional command spells to the Master who manages to defeat Caster and his Master.

According to Kotomine Kirei in Fate, his father died trying to protect him. As revealed in Fate/Zero, after Caster's defeat, Kayneth Archibald El-Melloi approached Risei to obtain additional command spells. After Risei reluctantly gives what Lord El-Melloi has come for, the Master shoots Risei and leaves him to die. As he dies, Risei leaves behind a message containing a secret password that will provide his son with all the remaining command spells Risei could give out. Kirei arrives to find his father dead and his father's final parting gift, and comes to the conclusion that Risei died trying to protect him. Though Kirei sheds tears realizing his father cared about him till the end, he finds himself feeling the same feelings he felt when his wife died - the desire to have seen them die.