Severyn Nalyvaiko (Северин Наливайко, Semen Nalewajko) (d. April 21, 1597) was a leader of the Ukrainian Cossacks who became a hero of Ukrainian folklore. The Decembrist poet Kondraty Ryleyev wrote a poem about him.
In 1594 Severyn joined a band of Cossacks who raided several Moldavian and Hungarian towns. The following year, Nalivaiko's Cossacks were joined by many run-away Ukrainian peasants and captured the town of Lutsk where his men massacred Polish nobility, Catholic clergy and local Greek-Catholics. From Volhynia Nalivaiko's Cossacks moved into Belarus, where they pillaged Mogilev.
Nalivaiko eventually offered peace to the Polish king Sigismund III Vasa, conditioned that that the Poles cede the lands between Southern Buh and Dniester rivers south of Bratslav to the Cossacks in exchange for their military service and loyalty to the Polish-Lithuanian Commonwealth. Having refused these terms, the king recalled Stanisław Żółkiewski from Moldavia to quell the Nalivaiko uprising, which had engulfed most of Polish crown lands in Ukraine and Belarus (that time called Ruthenia) by 1596. Nalivaiko joined his forces with the Cossack Hetman Hryhory Loboda (Polish: Hryhor Łoboda) but was forced to retreat to the Left-bank Ukraine. In May of 1596 the Cossack tabor was surrounded by Poles near the town of Lubny. The Cossacks fought for two weeks before running out of food and water. Thereupon they handed over Severyn Nalivaiko to the Poles in exchange for their own lives, only to be treacherously slaughtered by the Poles immediatedly after Nalivaiko's surrender. The Ukrainian national hero was brought to Warsaw in a cage and publicly quartered. The popular stories about his being crowned with a white-hot iron crown or boiled alive in a copper cauldron are not verified by factual evidence.