Ivan Sirko was a Ukrainian Cossack military leader and Koshovyi Otaman of the Zaporozhian Host, born around 1610 and died around 1680. He is believed to have co-authored the famous Cossack letter to the Ottoman sultan, which inspired the painting Reply of the Zaporozhian Cossacks by artist Ilya Repin. His place of birth is uncertain, but he is believed to have come from the Ukrainian (Ruthenian) Orthodox szlachta, a group of nobles. Sirko changed his political orientation several times throughout his career, sometimes supporting Moscow and sometimes fighting against it. He was known for his battles against the Poles, Tatars, and hetman Petro Doroshenko in alliance with Muscovy. Sirko was the first Cossack ataman to accept Kalmyks into his army.