He was born from the rock, where he emerged fully grown and holding his dagger and torch. He was famous for slaying a sacred bull.
There are seven rites of passage to gain entrance into the cult of Mithras. There are also seven levels of membership, the top level being the pater, who Annabeth Chase meets. If a person is an unbeliever, then they must die by fire or dagger.
Mithras' symbols are the torch and dagger, which one can be initiated into the cult with.
Aphrodite mentions Mithras as one of the deities that replaced Athena. Later, Annabeth Chase encounters a dozen ghosts, similar to the Lares of Camp Jupiter, in their sacred cavern of Mithras, when she follows the Mark of Athena, an owl. The ghost realizes Annabeth's disbelief and asks her to choose her path of death, or else Mithras will choose it for her.
However, Annabeth guesses their secrets: the rites of passage, levels of membership, and the ordeals. She bluffs that she is the 'magna mater' of the sisterhood of the child of Athena. The ghosts try to kill her, but Annabeth reminds them that they are dead. The pater says that Mithras will do it for them, and the statue on the altar begins to glow. The ghosts say that they cannot allow her to pass, as the weaver told them that she must be killed. She notices that the cavern is old and that the ceiling has cracks. Annabeth declares that she has power over the very stones, and strikes the capstone with her dagger. The Celestial bronze blade shatters the ceiling. The pater scoffs at her until suddenly the room shakes and the ceiling collapses on the altar and the pater. She slams with all her strength on the blocked entrance, and the bricks give way. She lunges out of the hole and finds herself falling into darkness.