was a class of daimyō (大名) in the Tokugawa Shogunate (徳川幕府) of Japan who were hereditary vassals of the Tokugawa before the Battle of Sekigahara. Fudai daimyō and their descendants filled the ranks of the Tokugawa administration in opposition to the tozama daimyō and held most of the power in Japan during the Edo period. Origins Fudai daimyōs originated from the families and clans who had served the prominent Tokugawa clan before its rise to national primacy during the Azuchi–Momoyama period in the late Sengoku period, including the Honda, Sakai, Sakakibara, Ii, Itakura, and Mizuno clans. A number of other clans which were not retainers of the Tokugawa before the Azuchi–Momoyama period also came to be counted as fudai, such as the Ogasawara and the Doi. Honda Tadakatsu, Sakakibara Yasumasa, Sakai Tadatsugu, and Ii Naomasa — Tokugawa Ieyasu's "Four Great Generals" — were all pre-Edo period fudai who went on to become fudai daimyōs. In addition, some branches of the Matsudaira clan, from which the Tokugawa clan originated, were classed as fudai while allowed to retain the Matsudaira name. Edo period (江戸時代) The birth of the fudai daimyō class began as Tokugawa Ieyasu (徳川家康) rose to power in Japan in the 16th century. Ieyasu's han (domains) increased as he gained prominence, and as his domains increased, he began to hand out landholdings to his vassals, so that one by one, many of them became daimyōs, the powerful feudal lords of the samurai warrior noble class. Ieyasu became the most powerful lord in Japan following victory at the Battle of Sekigahara in October 1600, displacing the Toyotomi clan and unofficially founding the Tokugawa Shogunate as his de facto military government with himself as the Shōgun. However, Ieyasu sought to consolidate his rule from potential usurpers, including the Toyotomi loyalists who were still fighting for Toyotomi Hideyori, the son and designated successor of Ieyasu's rival Toyotomi Hideyoshi, who had been an infant at the Battle of Sekigahara. The capital of the Tokugawa Shogunate was established in the eastern city of Edo, and Ieyasu filled his administration with fudai in fear of the tozama ("outside") daimyōs, who became Tokugawa vassals only after the battle. The fudai, in contrast to the tozama, typically ruled small domains in strategic locations along Japan's principal roads or in the Kantō region near Edo. High-ranking posts in the shogunate government (Bakufu) such as the rōjū, the wakadoshiyori, and