was a Japanese daimyo of the Sengoku period, and high-ranking government advisor, holding the title of Rōjū, and later Tairō. The son of Sakai Shigetada, Tadayo was born in Nishio, Mikawa Province; his childhood name was Manchiyo. He became a trusted elder (rōjū) in Toyotomi Hideyoshi's government, alongside Tokugawa Ieyasu. Under Hideyoshi, he was made lord of Kawagoe castle (in Musashi province, today Saitama prefecture) and later of Nagoya castle in Kyūshū's Hizen province. In 1600, in the lead-up to the decisive Sekigahara campaign, he fought against the Tokugawa at Aizu, and submitted to them at the siege of Ueda. Thus, having joined the Tokugawa prior to the battle of Sekigahara itself, Sakai was made a fudai daimyo, and counted among the Tokugawa's more trusted retainers. He served