The Berserkers are undead fairy warriors buried in the magic circle located in the Fowl Manor boundaries. They first appeared in The Last Guardian. They were raised to life by Opal Koboi after she had become "God-like" (As a result of her past self being killed along with black magic and nuclear fission). As of when they were entombed in the magic circle, they are spirits, waiting for the one who would unlock the Beserker Gate. When released, Berserkers posessed the body's of animals, mummies, or skeletons. They were enthralled to Opal when they were released. When they were released they did not realise just how much time had passed, and believed that what they were ordered to do by Opal was for the good of The People.
Oro of the Danu is the Captain of the Berserkers, and he inhabits the body of Beckett Fowl. He doesn't agree with Opal's motives and is constantly fighting his bonds. Other Berserkers are Bellico, who inhabits Juliet Butler and Gobdaw, who inhabits Myles Fowl and is extracted from there with a barrel of animal fat. The rest do not inhabit people, but wildlife, Chinese mummies, and pirate bodies.