Yemelyan Ivanovich Pugachev (also spelled Pugachyov; Russian: Емельян Иванович Пугачёв; c. 1742 – 21 January [O.S. 10 January] 1775) was an ataman of the Yaik Cossacks and the leader of the Pugachev's Rebellion, a major popular uprising in the Russian Empire during the reign of Catherine the Great.
The son of a Don Cossack landowner, Pugachev served in the Imperial Russian Army during the Seven Years' War and the Russo-Turkish War of 1768–1774. In 1770 he deserted the Russian military and spent years as a fugitive, gaining popularity among the peasants, Cossacks and Old Believers against a backdrop of intensified unrest. In 1773, he initiated open revolt against Catherine.