Berserker
The term Berserker comes from the Viking "Baer-sark", or "bear-shirt", referring to dreaded warriors who would dress themselves up in bearskins and likely worked as champions for Lords or Jarls, fighting duels in their stead (Point of contestation, Baer is not perfectly translated and could mean bare as in no clothes at all). Some even believed they could transform into bears, similar to the Ulfsark or "Wolf-Shirt" were believed to be able to turn into wolves, making them a possible origin for the myth of the werewolf. Similarly frenzied warriors appeared in many European Bronze and Iron Age cultures, like the Celts and Picts, with multiple sagas and poems explicitly using the word berserker. A 13th century Norse translation of a French story: "Yvain, Le Chevalier au Lion", translates the french word for champion into the Norse word for berserker, which gives it secondary meaning.
Tabletop Gaming
D&D's Barbarian class is based significantly on the concept of a Berserker, as well as on Conan (who himself by D&D lore is more of a Fighter with thief skills). Both games also have a Berserker-themed archetype for fighters; the Berserker in Pathfinder, and the Battlerager in 4th edition.
3rd edition had the Frenzied Besererker Prestige Class, notorious for being a prestige classes that actually makes you worse for taking it compared to not leveling up at all. This "honor" puts it next to the Blighter (who loses all Druid abilities to slowly gain back inferior version), most Book of Exalted Deeds prestige classes (which saddle the character with massive codes of conduct with penalties for violating beyond loss of class features), and a few Monk-like prestige classes (Which remove your ability to use weapons). Frenzied Berserker gets on that list by having the main class feature entail losing control of their character and attacking allies, and made worse (even though the first part is bad enough to make that list on its own) auto-failing dexterity base skill checks (meaning it is stopped by ordinary marbles).
4th edition also has the Berserker as a Variant Class for the Barbarian, trading the Barbarian's features for a completely new set of features. Weirdly, it's not technically an "Essentials Class", as it still uses the AEDU System!
Berserker is also the name of a ridiculous song performed by Love Among Freaks that appeared in the movie Clerks in 1994.