Kazimierz I, called The Restorer (1016-58), duke of Poland (1038-58). Son of Poland's King Mieszko II, Kazimierz succeeded his father in 1034 but was deposed by a rebellion of the nobles in 1037. The following year he returned to power as duke of Poland with the support of Holy Roman Emperor Conrad II, whom he then recognized as his overlord, as well as Henry III of Germany. Allying himself with Yaroslav the Wise, ruler of the Russian state of Kyiv, he subjected the Polish tribes to his rule and drove the Czechs from Silesia.