Hōjō Sōun (北條早雲?, 1432 – September 8, 1519) 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 reputable family of Shogunate officials. Although he only belonged to a side branch of the main, more prestigious Ise family, he fought his way up, gaining territory and changing his name in imitation of the illustrious Hōjō.
Traditionally Soun held a reputation of a ronin who rose to power almost overnight in Kanto; however, he belonged to a prestigious family in the direct employment of the Ashikaga shoguns, and enjoyed important family connections. His sister was married to Imagawa Yoshitada, a major daimyo from a prestigious cadet branch of the Ashikaga family. Shinkuro became a retainer in the Imagawa clan, and 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 in Izu province, he is credited by most historians as being the first "Sengoku Daimyo".
About 1475, under the cognomen of Ise Shinkuro, he worked for Imagawa, the constable of Suruga Province, and eventually became an "independent leader" with a number of warriors joining him. In 1491, he was able to take Horigoye after the death of Kanto Kubo Ashikaga Masatomo died, gaining control of Izu Province. He then adopted the surname of Hojo and the given name of Soun or Sozui. After building a stronghold at Nirayama, Hojo Soun secured Odawara Castle in 1494, the castle which would become the center of the Hōjō family's domains for nearly a century. In an act of treachery, he seized the castle after arranging for its lord to be murdered while out hunting. In 1516, he laid siege to the castle of Arai, and "was virtual master of all Sagami."
Sōun died the following year, and passed on the newly built Hōjō domains to his son Ujitsuna, who subsequently changed the clan name from the original Ise to Hōjō and posthumously renamed his father to Hōjō Sōun. In 1521, Ujitsuna built Sōun-ji temple dedicated to his father.