Hara Tanzan (???) (December 5, 1819 – July 27, 1892) was a Soto Buddhist monk, head monk at the Saijoji temple in Odawara and a professor of Philosophy at the University of Tokyo during the Bakumatsu and Meiji periods.
He was a forerunner of the modernization of Japanese Buddhism and the first (in Japan) to attempt to incorporate concepts from the natural sciences into Zen Buddhism.Hara was born in Iwakitaira Domain.
At the age of 15, Hara enrolled at the Shoheizaka Academy (??????) where he studied both Confucianism and medicine, the latter under Taki Genken.
At the age of 20 or 26, he entered Buddhist priesthood, though he would go on to study Western medicine later in life.Hara became the first lecturer of Indian Philosophy and Buddhist Studies at Tokyo University in 1879.
He was later superintendent of the Soto-shu Daigaku-rin (currently Komazawa University).Hara is featured in several koans.
He was well known for his disregard of many of the precepts of everyday Buddhism, such as dietary laws.