His full name was Bohdan Zynoviy Mykhailovych Khmelnysky.
There is no definite proof of the date of his birth, but according to Ukrainian historian Mykhaylo Maksymovych, it was likely 27 December, 1596 (St. Theodore's Day).
As it was custom in the Greek Orthodox Church, he was baptized by one of his middle names - Theodor, translated into Ukrainian has Bohdan.
Although the hetman was the highest military office and head of state in the Cossack Hetmanate, it was the second-highest military commander, after the monarch, in the Polish Commonwealth. Therefore, Khymelnystky was technically not a monarch.
In 1654, he concluded the Treaty of Pereyaslav with the Muscovite Tsardom, which eventually lead to the loss of independence to the Tsardom.
Bohdan Khmelnysky's banner was taken by the Polish at the Battle of Berestechko, which was then taken by the Swedes when they captured Warsaw in 1655. It can be currently viewed at the Armemuseum in Stockholm, Sweden.
In Ukraine, Bohdan Khmelnytsky is viewed as a national hero, and is depicted on a five Ukrainian hryvnia banknote. However in Poland, he is negatively viewed.
"Khmelnitski is not to be played with. In short, he has more brain, a stouter arm, and better luck than you, who are far too hasty." -- Page 17 of the Google Books edition of the novel With Fire and Sword.