Peter Ernst, Graf von Mansfeld, or simply Ernst von Mansfeld, was a German military commander; despite being a Catholic, he fought for the Protestants during the early years of the Thirty Years' War. He was one of the leading mercenary generals of the war.

The Thirty Years' War was one of the longest and most destructive conflicts in European history, lasting from 1618 to 1648. Fought primarily in Central Europe, an estimated 4.5 to 8 million soldiers and civilians died as a result of battle, famine, or disease, while parts of present-day Germany reported population declines of over 50%. Related conflicts include the Eighty Years' War, the War of the Mantuan Succession, the Franco-Spanish War, the Torstenson War, the Dutch-Portuguese War, and the Portuguese Restoration War.