Saint Nikolai of Japan, Nikolai Kasatkin (born Ioan Dimitrovich Kasatkin August 1, 1836 (Russian calendar); died February 16, 1912) was a Russian Orthodox priest monk and saint. He introduced the Eastern Orthodox Church to Japan. The orthodox cathedral of Tokyo (metropolitan diocese of Japan), Tokyo Resurrection Cathedral, is nicknamed Nikolai-do from his name by its neighbors, since he lived in its bishop's house.

Nikolai was born in August 1st, 1836 (as the Russian calendar) as a son of Dimitry Kasatkin, a Russian Orthodox deacon, in Smolensk prefecture. His mother died when he was five years old. He grew up into the hierarchy: in 1857 he entered to the Theological Academy in St. Petersburg. In July 7, 1860 (along the Russian calender) he became a monk and got the name of Nikolai. Nikolai was appointed as a deacon in July 12 in the same year, in the day of SS. Peter and Paul and at the next day July 13 was appointed as a priest, when the day of twelve Apostles, the commemoration day of the Chapel SS. Twelve Apostles belonging to the Academy.

In 1861 Nikolai landed at Hakodate, Hokkaido, Japan as a priest to the chapel of the Russian consulate in Hakodate. He was voluntarily appointed this duty since the day he had noticed a poster calling for a priest of this chapel when he had been a seminary student: he had begun to learn Japanese and quickly improved his mastery of the Japanese language. He converted three Japanese there. Later he moved to Tokyo, and made the city the see of the Bishop of Japan. His mission went throughout Japan: more than 250 churches were built from his mission. He was elected the first bishop of the Japanese Orthodox Church, and after the Russo-Japanese War was appointed archbishop.

During the war Nikolai stayed in Japan. Those days were very difficult for him because he could not hold mass since his love for his birthland Russia conflicted with his obligation as the bishop of Japan to pray for the Japanese Emperor and the Imperial Army and Navy. Nikolai therefore held no mass during the war but encouraged Japanese faithfuls both to pray for and to contribute to the Army and Navy. Some encouraged him to go back to Russia but he refused and worked eagerly for Japanese faithfuls and Russian captives. In a letter on the conditions of a camp in Hamadera, Osaka, Nikolai wrote of his astonishment at the Russians soldiers' illiteracy: nine of ten captives couldn't read. Nikolai sent priests and teachers to camps who educated and cared for the captives. His attitude and manners impressed not only orthodox faithfuls but also non-Christians. Even Emperor Meiji was impressed with his character, especially his Christian and diplomatic efforts between the Russian Imperial Household and the Japanese government. When the Russian Emperor Nikolai II had been the crown prince of Alexander III, young Nikolai II had visited Japan and was injured by a mentally-ill Japanese policeman, Otsu Jiken, Bishop Nikolai made a great effort to resolve this incident.