Proper noun.

A Slavic deity known for his appetite for destruction. Commonly associated with large thunderstorms, wars of mass destruction, and evil societies down fall (for example, the Bolshevik revolution, over throwing Nicholas the Second).

In modern day, typically mean a person you don't want to mess with, or they will most likely cause you great harm, either physical or mental.
"oh no! It's Yosko the Destroyer! Run for the hill!"
by Mad max the elegant March 5, 2012
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