Prince Jeremi Wiśniowiecki nicknamed Hammer on the Cossacks, was a notable member of the aristocracy of the Polish–Lithuanian Commonwealth, Prince of Vyshnivets, Lubny and Khorol 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. Wikipedia