Bohdan Zynoviy Mykhailovych Khmelnytsky (c. 1595 – 6 August 1657) was a hetman of the Zaporozhian Cossack Hetmanate of Ukraine. He led an uprising against the Polish-Lithuanian Commonwealth magnates (1648–1654) which resulted in the creation of a Cossack state. In 1654, he concluded the Treaty of Pereyaslav with the Tsardom of Russia, which led to the eventual loss of independence to the Russian Empire.
Note: In the series, his name is generally spelled Chmielnicki.
Bohdan Khmelnytsky was a minor officer among the registered Cossacks when the Ring of Fire brought Grantville back in history. A year or so after the Ring of Fire, Khmelnytsky was assassinated on his estate in Subotiv. His assassins were rumored to be three Poles, which in turn led to speculation that the Polish-Lithuanian Commonwealth may have obtained an up-time history book or had otherwise learned of Khmelnytsky's historical uprising.