sentences:  Holding the most important positions in the state and supporting young Grand Duke he became actual ruler of Lithuania until young Duke came of age and started his own policies as early as 1444.He successfully initiated the expansion of the Council of Lords' powers, made structural reforms, led assault on rebelling Kiev.When in 1444 Władysław died at battle of Varna, Polish politicians and leading lords insisted that Casimir should return to Kingdom of Poland and in 1445 the general assembly of nobility in Sieradz elected Casimir the new Polish king.