The Berserker is an enemy character from the Gears of War franchise. She cannot see, due to the darkness of the Locust underground tunnels, but is able to charge at enemies based on smell and a form of echolocation (also used by bats). In Gears of War, you encounter a Berserker several times. The only weapon known to kill them easily is the Hammer of Dawn. Berserkers are wild creatures, and in one instance, can be seen killing the Locust she was allied with. They were wiped out, along with the Kryll, in the lightmass bombing of the locust tunnel systems.
According to the Gears of War book Aspho Fields, Colonel Victor Hoffman claims that the Locust breed by chaining down the Berserkers and raping them to reproduce. Since Berserkers generally dislike obeying any orders, the male Locust must hold them down for their own survival.
The Berserker is a playable character in the Beast mode in Gears of War 3. She is an extremely powerful and resilient unit, but COG forces using flames and explosives can still bring her down. Berserkers are extremely efficient at destroying COG fortifications to allow the rest of the team to break through.
Strangely, Berserkers were not present in any capacity in Gears of War 2.