The Great Horned Rat, Lord Of The World Below or Under Father, is a minor god of Chaos. There have been others like him before, but none as strong or prolific in his presence.

The Great Horned Rat is kind of a big deal. Traditionally, the Warhammer settings have four Chaos gods: the violent Khorne, the scheming Tzeentch, the rapturous Slaanesh, and the plague-loving Nurgle.