Bolesław I Chrobry
The Kingdom of Poland has been traditionally dated back to c. 966, when Mieszko I and his pagan Slavic realm joined Christian Europe (Baptism of Poland), establishing the state of Poland, a process started by his Polan Piast dynasty ancestors. His oldest son and successor, Prince Bolesław I Chrobry, Duke of Poland, became the first crowned King of Poland in 1025.