Jeremi Wisniowiecki (Ukrainian: ????? ???????????? - Yarema Vyshnevetsky; 1612 – August 20, 1651) nicknamed Hammer on the Cossacks or Iron Hand, was a notable member of the aristocracy of the Polish-Lithuanian Commonwealth, Prince of Wisniowiec, Lubnie 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 Romanian origin, Wisniowiecki 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 Ruthenia and Ukraine (parts of the Polish–Lithuanian Commonwealth).
Wisniowiecki was a successful military leader as well as one of the wealthiest magnates of Poland, ruling over lands inhabited by 230,000 people.