Zero characters

Voiced by: Rikiya Koyama(Japanese); Matthew Mercer[1] Marianne Miller (Young Kiritsugu) (English)
Kiritsugu Emiya(衛宮 切嗣,Emiya Kiritsugu) is the master of Saber and the main protagonist. Born in Fuyuki City, Kiritsugu was raised on Alimango Island, where he lived with his father, Norikata Emiya, the fourth family head of the Emiya family and a magus specializing in time magic. He became friends with Norikata's assistant, a local girl called Shirley who was four years older than him, developing a crush on her. However, disaster struck when Shirley became a vampire after drinking one of Noritaka's potions. She pled for Kiritsugu to kill her, but he fled instead. Shirley subsequently lost control and turned all the residents of Alimango Island into vampires.
Their village was soon overrun by Executors from the Church and Enforcers from the Mages' Association, agents whose purpose was to destroy all the vampires and eliminate any trace of civilization and vampirism on the island respectively. Kiritsugu was the only survivor of the 'cleansing', saved by Natalia Kaminski, a freelance Enforcer who wanted information on the magus responsible. Returning to the hidden Emiya residence, Kiritsugu confronted his father on his research and Shirley's death. Realizing that his father had intended for the village to be his testing site for his research on immortality, Kiritsugu shot his father to prevent a similar tragedy from unfolding again in the future. He came under Natalia's wing and assisted her as she hunted down rogue magi. As they continued to eliminate dangerous threats to world peace and stability, Kiritsugu repeatedly eliminated the dangerous minority to save the majority. Eventually, during a mission gone awry, Kiritsugu chose to kill Natalia to prevent a worst-case scenario. It was then that he became disillusioned with the ideal of becoming a 'hero of justice', as he realized it was impossible to save one person without losing another.
Around eleven years before the fourth Holy Grail War, he took on a child soldier he had rescued as his apprentice, who he eventually named Maiya Hisau, training her in much the same way Natalia trained him. Two years later, Kiritsugu was hired by the Einzbern family to be their representative in the coming conflict. Believing that the Holy Grail could grant his wish for world peace, he left behind his former work. Despite being the true Master of the Einzbern family, Kiritsugu operates mostly in the background during the conflict, ambushing other Masters while they are otherwise occupied. Saber partners with Irisviel and acts out in the open to avoid conflict between Kiritsugu and Saber, as their methodologies conflict. Over the course of the War, Kiritsugu's mask of being a heartless assassin begs to crack, as he is torn between withdrawing from the war to live in peace with his family or sacrifice them to realize his wish of world peace. During his final fight with Kirei, Kiritsugu is dragged into the Grail. Grail's true nature (shown to have been corrupted) manifests, showing that it can indeed grant wishes but only via methods that the user already knows. Kiritsugu realizes that the Grail would interpret his wish by killing off every last person on earth except for himself and his family. Steeling himself, Kiritsugu kills the illusions of his family that the Grail shows him and declares that he save the world. Upon returning to reality, he orders Saber to destroy the Grail. However, the Grail is unable to be destroyed and its corrupted nature causes a huge fire. Kiritsugu desperately looks for survivors, discovering an amnesiac boy who he names Shirō and adopts. Kiritsugu then spends months trying to retrieve his daughter Illya, but the Grail's curse robbed him of his magical abilities and physical health while Acht strictly trains Illya to become the next vessel under the impression that her father abandoned her. Years pass as Kiritsugu wastes away from the curse. As his life fades, while watching the moon with his adopted son, Kiritsugu talks about his dream to become a hero and how he hadn't been able to after becoming an adult; he believes that he had been a failure in his life. Shirō, however, ends up taking his father's dream to heart and declares that he will take up Kiritsugu's dream (setting the backstory for the Emiya family in Fate/Stay Night). Kiritsugu realizes that Shirō will not make the same mistakes that he did, and quietly passes away with contentment.

Question: Who is the main character of Fate/Zero?
Answer: Kiritsugu Emiya