Today, to be or to go berserk means to be frenzied, crazed, and the word and phrase carries a connotation of violence. The phrase to go berserk is relatively recent, only dating to the opening years of the twentieth century, but the noun and adjective is about a hundred years older than that, or at least it is in English usage.
The word comes from the Icelandic berserkr, meaning a powerful Norse warrior who displayed a wild and uncontrolled fury on the battlefield. In other words, a stereotypical Viking, or at least how Vikings appear in modern, popular imagination. The etymology of the Icelandic word is disputed, but it probably comes from bear + sark, a type of shirt or tunic. So a berserk or berserker was literally a bearskin-clad warrior.
Copyright 1997-2013, by David Wilton