You have killed a large number of people. This is generally not a good thing to get known for. People from the wrong side of the track will like you a little more, however.”— Fallout and Fallout 2 description
You get this title by killing many good karma people and having bad or very bad karma.
Theoretically, bad characters have a better reaction in dialogue. However, no critters are actually flagged as evil in the game, meaning the only effect the Berserker reputation has are unique dialogue options and reactions from NPCs. NPC reaction may be initially lower to Berserkers.
- What do you want?
- To see a valley filled with my enemies' heads mounted on spears. A silent valley, except for the wind whistling through their ears.”— Zark and the Berserker Vault Dweller