Сигизмунд II Август
He was a close advisor to King Sigismund II Augustus, and supported many of his plans, including the one to divorce Catherine of Austria. He threw his weight behind the pro-reform camp, and was actively involved in bringing about the transformation of the Polish–Lithuanian union into the Polish–Lithuanian Commonwealth. He represented King Sigismund II Augustus in negotiations with Lithuanian magnates in Vilna, and he took part in the Lithuanian Sejm in Bielsk Podlaski of 1564.