The Berserker was an alien added in the privately published 1978 expansion by Alan Emrich. No Flares are known for it.
You have the power to go berserk. When you are the offensive player in a challenge, you may challenge any or all of the players on a planet in the defender's home system. You decide which of the defending players will represent his side with his Alien Power, hand, etc. Players directly challenged may not ally in any way. In addition, any time you play a Compromise card, it is treated like an Attack 15 card. If changed by Edicts or Alien Powers, your cards will be treated like normal Compromise cards.
The Berserker has two unrelated powers, making him a little clunky. His ability to turn his Compromise cards into Attack 15s is interesting in that it both weakens and strengthens him in differenet ways. His ability to attack multiple targets in the defender's system is a little like a weaker Will. By attacking multiple races he can ensure that they can't ally with more tokens than they have on that planet, and of course he can target the weak.