Mithras was a popular Roman god in the 2nd to 4th centuries CE. He was based on Mithra, the most important god in ancient Persian polytheism.
The Persian Mithra was a god of contracts (which is the literal meaning of his name) and all things associated with contracts: justice, friendship, cattle-herding and the sun (which beholds all things and thus can ensure the keeping of oaths).
Since Zoroaster (6th century BC) denounced the sacrifice of the bull, it is likely this was a ceremony practiced by the ancient worshippers of Mithras.
In Roman Mithraism, Mithras was a sun god (called sol invictus, "the invincible sun"), a "bull-slayer," "cattle-thief" and the savior of initiates of his cult. He was probably also the god of kings and of war (which explains Mithraisms' popularity among soldiers).
Mithras Slaying the Bull
The image of Mithras killing a bull is central to nearly all Mithraic temples, and thus provides an important (but difficult) clue to the beliefs and concepts of Mithraism. Mithras is dressed like a Persian, including a distinctive cap. He is shown astride a bull, plunging a dagger into its flank. The bull's tail becomes an ear of wheat at the end. The scene takes place in front of a cave.
Mithras is accompanied by a dog, snake, scorpion and raven, as well as two minor deities who are also dressed in Persian attire. Each carries a torch (one pointed up, one down) and their names are known from inscriptions: Cautes and Cautopates. Above the scene are images of Sol and Luna (Sun and Moon).
