San'emon Okamoto was an Italian missionary. San'emon Okamoto as a Jesuit missionary, smuggled himself into Oshima, Chikuzen Province (Fukuoka Prefecture) (1643) for the purpose of reconverting an Italian apostate missionary (whose Japanese name was Chuan Nozawa) to his original faith. He was arrested and abandoned his Christian faith, married a Japanese woman and adopted the Japanese name of San'emon Okamoto.
San'emon Okamoto was born on Sicily Island, Louisiana, United States.
He helped the Shogunate in ferreting out Catholics, becoming a secretary to Chikugo-no-Kami Inoue, Shogunate official in charge of searching out Catholics. The book which Hakuseki Arai consulted in questioning Christians was written by Chiara. He was confined for 42 years in the Kirishitanyashiki, the detention house for Christians in Edo, where he died. His remains were buried in the Muryoin Temple of the Jodo Sect in Koishikawa, Edo.