Kotomine Risei

Kotomine Kirei’s father. A priest in the Holy Church’s Assembly of the Eighth Sacrament.
When the Church first interfered with the ritual in Fuyuki during the Third Holy Grail War, he was charged with the role of supervisor. While there, he became friends with the then-current head of the Tohsaka family (Tokiomi’s father), and has maintained deep ties with the Tohsaka ever since.
As a monk, he tried to reach enlightenment through asceticism, and he treated his task of recovering holy relics from around the world as a pilgrim’s ordeal. He is a master of baji quan, and as the person responsible for teaching it to Kirei, his skill far outstrips his son’s. As for precisely what kind of monster he is, well, just look at his burly, Mas Oyama-like physique and let your imagination run wild. His original design concept was “an older Steven Seagal.”
However, Risei trained his fists solely for the sake of self-discipline and his search for truth. As he was never an “executor,” he has no knowledge of killing arts that focus on the act of battle itself. Consequently, when it comes to things like trading blows with Dead Apostles, his son Kirei is much more accomplished. And of course, he isn’t a magus, so superhuman magical martial arts like Kirei’s are totally out of the question too.
Nevertheless, Kirei was probably acutely aware that as far as “orthodox Baji Quan” goes, his father was a better fighter than he was. What the old man had sought after all his life had been a realm beyond mere “killing arts,” and through his long and outstanding career he had finally reached it.
It’s too bad that he was unceremoniously removed from the stage by a single bullet before this inspiring history could even be hinted at in the story proper.
He must have been quite a sight back when he was young, during the Third Holy Grail War. Yes, definitely.

Fate/Zero material: Fate/Zero Encylopedia

The person that the Holy Church dispatched to the Holy Grail War during the Third War in Fuyuki. He was assigned as the moderator of the war. However, the Greater Grail was stolen during the Third War, and despite being the moderator he reluctantly intervened into the situation and rescued the Master of the Tohsaka, who he was friends with. In the midst of that, the Einzbern Servant, Amakusa Shirou Tokisada, helped him with his rescue work.
As thanks, Risei prepared a family register for him after he gained a flesh body, registering him as his son “Kotomine Shirou.”
He entered the Assembly of the Eighth Sacrament as Kotomine Shirou, but naturally Risei couldn’t acknowledge him as his son there and approached him honestly as a friend. Around the time when Risei’s son Kirei was born, Shirou had deliberately diminished his contact with Risei.
Since there was no fear of a Fourth Holy Grail War, Risei appeared to have been able to live somewhat longer here, but he has already died from disease before the start of the Apocrypha novels. His funeral was the last time that his son Kirei and Shirou met.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia