Mansfeld, Peter Ernst von (pāˈtər ĕrnst fən mänsˈfĕlt) [key], 1580?–1626, military commander in the Thirty Years War. Illegitimate son of a governor for the Hapsburgs in Luxembourg, he rendered distinguished service in the imperial forces in the Netherlands and was legitimized; by 1607 he was styling himself count. At the beginning of the Thirty Years War, Mansfeld and his army were loaned by his employer, the duke of Savoy, to Frederick the Winter King, in Bohemia. Frederick's funds ran low, however, and shortly before the battle of the White Mt., Mansfeld refused further service. A promise of Dutch funds later induced him to defend Frederick's possessions in the Palatinate. He was at first successful and proved himself skillful in command. He won an engagement with Tilly in 1622, but he was unable to oust the imperial forces, and his unruly men ravaged and terrorized the country. Frederick dismissed him. He became (1623) a mercenary leader for Holland and in 1625, with a subsidy from England, recruited a force to fight on the Protestant side. He was severely defeated (1626) by Wallenstein near Dessau. Mansfeld attempted then to cooperate with Gabriel Bethlen but without success.