Berserkers were a warrior race who were the inspiration behind berserkers. They visited Earth at some point, where they were encountered by Vikings and mistaken for human warriors wearing animal skins.
The Berserkers created special pendants, which they made to expand their armies. The pendants would allow people to control other people, and with every person they controlled they would become more like a Berserker. At least one Berserker Pendant was left on Earth. It fell into the hands of Jacob West, and later, Paul Langer. (SJA: The Mark of the Berserker)