was the first head of the late Hōjō clan, one of the major powers in Japan's Sengoku period. Born Ise Moritoki, he was originally known as Ise Shinkurō, a samurai of Taira lineage from a family of little importance or power, he fought his way up, gaining territory and changing his name to the illustrious Hōjō.
According to some sources, he was a lowly samurai or ronin, but he had some important family connections. His sister was married to Imagawa Yoshitada, a member of a fairly powerful samurai family. When Yoshitada died in battle in 1476, Shinkurō mediated the succession dispute between supporters of Yoshitada's son Imagawa Ujichika and Yoshitada's cousin, Oshika Norimitsu. This proved a temporary peace. When Norimitsu again attempted to gain control of the Imagawa clan, Sōun came to Ujichika's defense, killing Norimitsu. Sōun was rewarded by Ujichika with Kokukuji castle. He gained control of Izu Province in 1493, avenging a wrong committed by a member of the Ashikaga family which held the shogunate. With Sōun's successful invasion is Izu province, he is credited by most historians as being the first "Sengoku Daimyo".
Soon afterwards, he secured Odawara, the castle which would become the center of the Hōjō family's domains for nearly a century. Supposedly, he seized the castle after arranging for its lord to be murdered while out hunting. Sōun then took Kamakura, the old Shogunal capital, in 1512, and the castle of Arai in 1518.
Sōun died the following year, and passed on the newly build Hōjō domains to his son Ujitsuna, who subsequently changed the clan name from the original Ise to Hōjō and postumously renamed his father to Hōjō Sōun.