Casimir II,1138–94, duke of Poland (1177–94), youngest son of Boleslaus III. A member of the PiastPiast
, 1st dynasty of Polish dukes and kings. Its name was derived from that of its legendary ancestor, a simple peasant. The first historic member, Duke Mieszko I (reigned 962–92), began the unification of Poland and introduced Christianity.
..... Click the link for more information. 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.