Cossacks are a traditional community of people living in the southern steppe regions of Eastern Europe (primarily Ukraine and southern Russia) and Asian Russia. They are famous for their self-reliance and military skills, particularly horsemanship. "Cossack" may also refer to a member of a Cossack military unit. Originally Cossacks were runaway Ruthenian peasants who escaped Polish and Russian feudal pressure and settled in the southern steppes.
Different Cossack groups are identified with different hosts, or regions. The Cossacks of the Zaporozhian, Don, Terek and Ural hosts, as well as areas of Siberia (such as the Baikal Cossacks) are the best known. Cossacks first became widely known in western Europe in the mid-17th century as a result of the great revolt of Bohdan Khmelnytsky and the Zaporozhians against the Polish-Lithuanian Commonwealth in what is now Ukraine, which shook the geopolitical foundations of eastern Europe.