A Slavic warrior caste known throughout Russia, Ukraine and Northern Mongolia. The name Cossack probably originates from Turkic, "Kazakh" meaning either "horseman" or "free man" (i.e. not a serf or noble) depending on context. Both definitions hold true, as Cossack warriors were exclusively cavalry, and actively recruited freed or runaway serfs into their ranks. Going by the Turkic/Mongolian origin of their name, the Cossacks may have originated in Central Asia, and migrated into the Slavic lands as nomads, perhaps on the heels of the Mongol invasions.

Historically, the Cossacks were predominantly Russian Orthodox Christian, but there were a few, especially around Crimea, who were Muslim, and some were even Buddhists from Mongolia.

Most early accounts of the Cossacks come from those who fought them, and recount their brutality and the use of bull whips as a battlefield weapon. Later accounts come from Russian officers who fought alongside the Cossacks during Napoleon's invasion of Russia. The Cossacks fought alongside the Russian army as late as WWI. In the Revolution, the Cossacks aligned with the Czar, and committed numerous acts of brutality against anyone suspected of Communist sympathies. They also carried out pogroms against Jewish villagers, under the assumption that all Jews were Communists. After the Revolution, the Cossacks were persecuted by the Bolsheviks and finally crushed by Stalin.