Yermak Timofeyevich
The Don Cossack Army, an autonomous military state formation of the Don Cossacks under the citizenship of the Moscow State in the Don region in 1671-1786), began a systematic conquest and colonization of lands to secure the borders on the Volga, the whole of Siberia (see Yermak Timofeyevich), and the Yaik (Ural) and Terek rivers. Cossack communities had developed along the latter two rivers well before the arrival of the Don Cossacks.