Sessai Chōrō (雪斎長老, 1496 - 1557), more commonly known as Taigen Sessai, was a Japanese Yamabushi (mountain ascetic) who held a position similar to "abbot" of a Buddhist temple. As the uncle of Imagawa Yoshimoto, Sessai often advised his nephew and eventually became a full time military advisor for the Imagawa Clan. Sessai was instrumental in the Imagawa's military and political victories over the Matsudaira clan of Mikawa. It was during this time that Yoshimoto came into direct conflict with Oda Nobuhide of Owari, being defeated by the aggressive warlord at the first battle of Azukizaka in 1542. After this setback, Yoshimoto left control of his military forces to Sessai who would go on to defeat Nobuhide at the second battle of Azukizaka in 1548.
By 1551, Sessai had managed to secure Matsudaira Takechiyo, known also as Matsudaira Motoyasu and later as Tokugawa Ieyasu, as a hostage. He managed this by besieging the castle of Oda Nobuhiro, the illegitimate eldest son of Nobuhide and entering negotiations with his younger brother, the famous Nobunaga. Motoyasu would serve as a crucial vassal for the Imagawa until their defeat at Okehazama. Sessai was instrumental in the creation of the "triple alliance" between the Imagawa, Hōjō and Takeda Clans. At some point, Sessai was a tutor for the young Motoyasu although to what extent is unknown. In 1557, Sessai died in Chokei-ji temple due to complications of gout.