Mithras (i.e. the Friend), the highest of the second order of deities in the ancient Persian religion, the friend of man in this life and his protector against evil in the world to come, sided with Ormuzd against Ahriman, incarnated in the sun, and represented as a youth kneeling on a bull and plunging a dagger into his neck, while he is at the same time attacked by a dog, a serpent, and a scorpion.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Mitford, William * Mithridates the Great