Sakai Tadayo (酒井 忠世; July 14, 1572 – April 24, 1636) was a Japanesedaimyō of theSengoku period, and high-ranking government advisor, holding the title ofRōjū, and laterTairō.
The son ofSakai Shigetada, Tadayo was born inNishio,Mikawa Province; his childhood name was Manchiyo. He became a trusted elder (rōjū) inToyotomi Hideyoshi's government, alongsideTokugawa Ieyasu. Under Hideyoshi, he was made lord ofKawagoe Castle (inMusashi Province, todaySaitama Prefecture) and later ofNagoya Castle inKyūshū'sHizen Province. In 1600, in the lead-up to the decisiveSekigahara campaign, he fought against the Tokugawa atAizu, and submitted to them at thesiege of Ueda. Thus, having joined the Tokugawa prior to the battle of Sekigahara itself, Sakai was made afudai daimyō, and counted among the Tokugawa's more trusted retainers. He served under Ieyasu for a time, and under the second shōgun,Tokugawa Hidetada, as ahatamoto.
Sakai's father died in 1617, and so he inherited his father's domain ofMaebashi inHarima Province, which had been assessed at 33,000koku, and was now changed to 85,000koku by the shogunate. In 1632, following a shakeup of positions within the bureaucracy, Sakai becamenishi no marurusui, placing him in charge of the western districts ofEdo Castle, the seat of the shogunal government. Two years later, the Western districts were burnt down while the shōgun was away in Kyoto. Sakai was stripped of his position, and exiled toKan'ei-ji.
Appealing to theGosanke (the heads of the three branch families of the Tokugawa), Sakai was invited to return to the castle two years later, in 1636. Along withDoi Toshikatsu andSakai Tadakatsu, he was appointed to the newly created post ofTairō (Great Elder). He died within weeks of being appointed, however, at the age of 64. His eldest son,Sakai Tadayuki, died around the same time, and so the next oldest son,Sakai Tadakiyo succeeded his father.