Since I did Cerberus for C, I thought it was appropriate to do Cerberus' brother, Orthrus for O.
Instead of having three heads, Orthrus only had 2 heads. From the Greek myths, this dog guarded the red-purple cattle of the tree-bodied giant, Geryon in the "sunset" land of Erytheia ("red one"), one of the isands of the Hesperides in the far west of the Mediterranean. It spotted Hercules trying to steal the cattle and warned its owner. Orthrus fought Hercules with the help from the centaur, Eurytion, but the dog was defeated and clubbed to death.