Cowsius Clay
, or Cauwsiuclay (as spelled in his poster) is a cow, a bully, and the leader of a gang of cows in Spain called the Mooers. He only appeared in The Reign in Spain.

Cowsius is undefeated in 800 boxing matches, and killed many of his opponents. His promoter and manager is King Don, who is conspiring with him on a real estate scam and is always betting on him.

When the dragons of Camelhot came to Spain, Flicker fought against Cowsius, and Flame gave him a red cape that Blaze bought at a shop. Cowsius was enraged by the red cape and attacked it rather than Flicker, eventually slamming into a dead cow hanging from the ceiling, which dazed him. Flicker knocked him to the ground and won the battle.

Cowsius's fate after the battle is unknown.