Free warrior peasants of east Slavonic descent who served as cavalry under the tsars?

The free warrior peasants of East Slavonic descent who served as cavalry under the tsars are known as Cossacks. They played a significant role in the military and social landscape of Russia, particularly from the 15th century onward. Cossacks were known for their horsemanship, independence, and fierce loyalty to the tsar, often acting as frontier guards and explorers. Their unique culture and traditions have had a lasting impact on Russian history and identity.