Alexander of Masovia (pl: Aleksander mazowiecki; 1400 - 2 June 1444) was a Polish prince member of the House of Piast from the Masovian branch. He was Bishop of Trento since 1425, titular Patriarch of Aquileia since 1439, Cardinal nominated by Antipope Felix V as titular of the diocese of St. Lawrence at Damascus (San Lorenzo in Damaso) since 1440, titular Bishop of Chur since 1442 and rector at St. Stephen's Cathedral, Vienna since 1442, a diplomat.
He was the second son of Siemowit IV, Duke of Masovia and Alexandra of Lithuania, daughter of Algirdas.
Despite being the second son of his family, from early childhood Alexander was destined for a Church career. To this end, he was sent at the court of his maternal uncle, King Władysław II Jagiełło at Kraków, where under his tutelage begin his studies. Thanks to the royal protection, in 1414 he was already named Provost at Gniezno Cathedral.
During 1415-1422, Alexander assisted at the University of Kraków, where, however, wasn't an excellent student. In any case, he was unable to finish any study. Nevertheless, at the end of 1422 and thanks to being a relative of the King, he was elected honorary rector, which was contrary to the university laws.
In 1422 Władysław II Jagiełło made an unsuccessful attempt to appointed Alexander in the Bishopric of Poznań. However, the King wasn't discouraged by the failure and the following year, he managed to obtain from Pope Martin V a different diocese to him, Trento, who was located on the border between Italy and Germany. Only then Alexander decided to be ordained as priest and went on the long journey to his new diocese.