Simplify the following text for a Grade 5 native English-speaking person.
Original: Casimir I the Restorer ( ; b. KrakÃ w , 25 July 1016 - d. PoznaÅ , 28 November 1058 ) , was a Duke of Poland of the Piast dynasty and the de facto monarch of the entire country since 1034 until his death .
Simplified: Casimir I the Restorer ( ; b. KrakÃ w , 25 July 1016 - d. PoznaÅ , 28 November 1058 ) , was a Duke of Poland . He was a part of the Piast dynasty .