Skaven

The Skaven are a vile and innumerable race of humanoid rats that infest the tunnels beneath the Old World, dwelling in a vast subterranean realm they call the Under-Empire. Driven by ambition, paranoia and unending hunger, they scheme and squabble in the dark, their teeming warrens sprawling beneath the very cities of men, dwarfs and elves who mostly refuse to believe such a menace could truly exist.

Skaven society is a seething chaos of backstabbing and betrayal, ruled in name by the Council of Thirteen and driven by the corrupting power of warpstone, a substance both fuel and poison to their kind. The clans of the Skaven each pursue their own dark craft: Clan Skryre unleash insane warp-lightning weapons, Clan Pestilens spread rot and plague, Clan Moulder flesh-craft monstrous rat-ogres, and Clan Eshin train assassins who kill in silence.

For all their cowardice and treachery, the skaven are terrifying in their sheer numbers, breeding faster than any race can hope to cull them. A single skaven is a scheming coward who will flee at the first sign of danger, but a swarm of tens of thousands, driven forward by the lash and their own frenzy, can drown a city in fur, blades and disease. They dream, always, of the day the Great Horned Rat's children rise to devour the surface world entire.