They were a very odd band of pirates who first appeared pillaging the northern shores of the Unicorn Forest (in the episode The Terror of Hammerhand). They have a habit of repeating certain words or phrases three times.

The original Berserkers were apparently all killed when their ship was sank, but Hammerhand was later mystically resurrected by Mumm-Ra, who summoned up his spirit to animate a clone of Panthro which he had created. When the plan failed, Hammerhand's spirit broke Mumm-Ra's control, and the clone body shifted into Hammerhand's original form before departing.

When he next appeared, in the Season 2 mini-series, "ThunderCats-Ho!", Hammerhand had reformed the Berserkers with new members endowed with cybernetic bodies and powers like his own.