Mithras (ミトラス, Mitorasu)?, sometimes confused with the Zoroastrian/Vedic Mithra or Mitra, is a demon in the series of Greco-Roman origin. While designs of Mithras and Mithra in the series were originated from the Roman Empire, this article focuses on the entity of Roman origin.
Mithraism was a religion worshiping the god Mithras originated from the Roman Empire from about the 1st to the 4th century. It is believed that the cult was popular in the Roman military and did not accept female disciples. Whether the god was directly inspired by the much older Mithra from Persia remains debatable. It is today considered a mystery religion due to lack of textual records of the cult, but many Mithraic temples and artifacts survive.
The series design that first appeared in Soul Hackers is faithful to the religious figure: being born from a rock as an adult and holding a knife which would be used for bull-slaughtering, a ritual believed to be commonly practiced by the disciples in honor of the god.
"A sun deity who was worshiped in the Roman empire from the 1st to the 4th century AD. The rituals of the religion were secretive, but it is believed that they had to do with covering oneself in the blood of sheep and bulls. He was said to be reborn after death, and a festival was held on the winter solstice for him."
—Shin Megami Tensei: Strange Journey compendium
Mitra is the master of Sector Bootes and is introduced as Master Mitra, appearing in a form possessed in earlier titles at first. He and his servants have been "recruiting" members of the expedition by threat or force and appears to be interested in the protagonist and offers him a chance to join him in return for being made a citizen of Mitra's domain in the new world to come, an invitation he extends to everyone aboard the Red Sprite as well.
The Red Sprite crew uses the Luxury Bell Mitra provided the protagonist with and creates a diversion allowing him to reach the higher levels of his tower and do combat with him. Upon his defeat, he drops Bootes' Rosetta and a Rare Forma. Later, when traversing Sector Delphinus, it becomes apparent Sectors Bootes and Delphinus have been collaborating for extended periods on human experimentation, as seen when upon reaching Mitra's private laboratories, a trophy, the Madman's Stone, has a plaque explaining the bond between Mitra and Asura, Delphinus' master.
"A sun deity who was worshipped in the Roman Empire from the 1st to the 4th century AD. He was said to be reborn after death, and a festival was held on the winter solstice for him."
—Persona 5 compendium
Shadow Makigami takes the form of Mithras during the request, "Phantom Thieves VS Burglary Ring." He will summon an Oni and Onmoraki to aid him in battle, and will also attempt to buff them with Tarukaja.