Petro Kalnyshevsky (20 June 1690? - 31 October 1803) was the last Koshovyi Otaman of the Zaporozhian Host, serving in 1762 and from 1765 to 1775. Kalnyshevsky was a hero in the Russo-Turkish War of 1768-1774 for which he was awarded with the gold medal of the order of St.Andrew with diamonds for courage and the rank of lieutenant-general.
Being the leader of the Zaporozhian Host, Kalnyshevsky defended the rights of Cossacks and their independence from increasing Imperial Russian influence, and encouraged agricultural development and trade in the Zaporozhian steppe.
After the destruction of the Zaporizhian Sich, Kalnyshevsky was arrested, tried and in July 1776 incarcerated at Solovetsky Monastery, with the strict prohibition of correspondence or socialization with anyone. In 1792, he was transferred to solitary confinement at the Povarnya jail, where he remained until 1802. When his cell was opened it was discovered that it had feces two arshins (nearly three feet) deep.
Being pardoned by Emperor Alexander at the claimed age of 110 years, Kalnyshevsky (already blind at that time) decided to remain in the monastery, where he died two years later in 1803.