Prince Jeremi Wiśniowiecki ( – Yarema Vyshnevetsky; 1612 – 20 August 1651) nicknamed Hammer on the Cossacks (), was a notable member of the aristocracy of the Polish–Lithuanian Commonwealth, Prince of Wiśniowiec, Łubnie and Chorol in the Crown of the Kingdom of Poland and the father of the future King of Poland, Michael I. A notable magnate and military commander with Ruthenian and Moldavian origin, Wiśniowiecki was heir of one of the biggest fortunes of the state and rose to several notable dignities, including the position of voivode of the Ruthenian Voivodship in 1646. His conversion from Eastern Orthodoxy to Roman Catholicism caused much dissent in Ruthenian (Ukrainian) lands (part of the Polish–Lithuanian Commonwealth). Wiśniowiecki was a successful military leader as well as one of the wealthiest magnates of Poland, ruling over lands inhabited by 230,000 people. Biography Youth Jeremi Michał Korybut Wiśniowiecki was born in 1612; neither the exact date nor the place of his birth are known. His father, Michał Wiśniowiecki, of the Ruthenian Wiśniowiecki family, died soon after Jeremi's birth, in 1616. His mother, Regina Mohyła (Raina Mohylanka) was a Moldavian-born noble woman of the Movilești family, daughter of the Moldavian Prince Ieremia Movilă, Jeremy's namesake; she died in 1619. Both of his parents were of the Eastern Orthodox Church rite; Jeremy's uncle was the influential Orthodox theologian Petro Mohyla, and his great-uncle was Gheorghe Movilă, the Metropolitan of Moldavia. Orphaned at the age of seven, Wiśniowiecki was raised by his uncle, Konstanty Wiśniowiecki, whose branch of the family were Roman Catholics. Jeremi attended a Jesuit college in Lwów and later, in 1629, he traveled to Italy, where he briefly attended the University of Bologna. He also acquired some military experience in the Netherlands. The upbringing by his uncle and the trips abroad polonized him, and turned him from a provincial Ruthenian knyaz into one of the youngest magnates of Poland and Lithuania. In 1631 Wiśniowiecki returned to the Commonwealth and took over from his uncle the management of his father's huge estate, which included a large part of what is now Ukraine. In 1632 he converted from Eastern Orthodoxy to Catholicism, an action that caused much concern in Ukraine. His decision has been analyzed by historians, and often criticized, particularly in Ukrainian historiography. The Orthodox Church feared to lose a powerful protector, and Isaiah Kopinsky, metropolitan bishop of Kyiv and a friend of his mother, unsuccessfully