Casimir II, 1138–94, duke of Poland (1177–94), youngest son of Boleslaus III. A member of the Piast dynasty, he drove his brother Mieszko III from power at Kraków in 1177 and became the principal duke of Poland. At the Congress of Leczyca (1180) the nobility and clergy, in return for privileges he had granted them, vested Casimir's descendants with hereditary rights to the crown. Casimir himself was never crowned king.
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