A Cossack is a member of a mixed-ethnicity group from southern Russia, Central Asia, or the Ukraine. The Cossacks are renowned as cavalry fighters, and served the Tsars of Russia from the late 18th century until the Russian Revolution.
The word cossack comes from the Turkic kazakh or qazag, meaning "freeman" or "adventurer." The Cossacks may descend from a western group of Turkic Kazakhs who mingled with Eastern European Slavic people.
"Some of the Don Cossacks so hated Soviet Russia that they collaborated with the Nazis during the Second World War."