Honinbo Sansa was a Buddhist priest of the Nichiren sect and his dharma name was Nikkai. He lived in a temple pavilion called Honinbo, where he taught go and shogi. After becoming Meijin, he took the name of Sansa.
"In 1588, Nobunaga's successor, Toyotomi Hideyoshi, organized a large-scale competition to systematize the rankings of Go players. Nikkai, a high-ranking Buddhist monk, who was Nobunaga's Go teacher, won this competition and Hideyoshi decreed that from then on all other players should take black or a larger handicap from him. Nikkai was also awarded a stipend which began the government patronage that enabled go to flourish in Japan." (Bozulich, 1999) 
For many years it was believed that Honinbo Sansa had a rivalry with a person named Kashio Rigen. However, evidence referred by Fairbairn & Hall (2009, p. 198-9) suggests that in all probability the name Kashio Rigen was a confusion based upon another text, where the two names Kashio and Rigen are immediately next to each other. This would mean that Kashio and Rigen are different people and Honinbo Sansa had a rivaly with two individuals, rather than a single person.
 Fairbairn, J. & Hall, T. M. (2009). The Go companion: Go in history and culture. Richmond, VA: Slate & Shell.