A contingent of rebellious young “gods” who were disenfranchised after the general cultural fall of the Norse Mythos empire. Somewhere along the line, they became less about “go out and have fun” and more about “kill what you find, especially if it’s a challenge.”
They’re deeply feared, and fortunately, usually run in worlds other than Earth. Humans, after all, make really lousy prey. They first show up in The Christmas Dragon.