Shōkū (証空?, November 30, 1177 - December 24, 1247), sometimes called Seizan (西山?) was a disciple of Hōnen, founder of the Jōdo-shū Buddhist sect. Shōkū later succeeded another disciple of Hōnen, Jōhen as the head of a former Shingon Buddhist temple, Eikandō, established a separate branch of Jōdo-shū called the Seizan branch (after its namesake), and completed the transition of Eikandō from a Shingon temple into a Jōdo shū one.
Read more about Shōkū: Biography