The Legend of Mitra, the only good God of the Mythos.
A Human image of Mitra the All Seeing.
In the Works of Howard
Mitra is one of the few good deities of Hyboria, and is by far the most worshiped. Mitra is a god of humility, forgiveness, and kindness. Think of him as a fictionalized god of the Israelites and precursor to Christ. Keep in mind, in the Mythos, the God of the Hebrews, Christians, Muslim and others don't exist in the works of H.P. Lovecraft as the faithful believe. Though in the context of the fictional worlds of Lovecraft and Howard it's quite apparent that Mitra is the entity Rabbi's and Priests pray to in the stories.
Mitra's religion is a monotheistic one, and while his followers do not persecute other religions they are very skeptical and wary of them.
Mitra's temples and alters are intentionally unadorned, reflecting a simple ascetic lifestyle free from decadence and greed. Prayers for Mitra's favor are often made, but sacrifices are neither encouraged or even approved of. Howard Writings “Well,” he said presently, “suppose we admit the former existence of cults revolving about such nameless and ghastly gods and entities as Cthulhu, Yog Sothoth, Tsathoggua, Gol-goroth, and the like, I can not find it in my mind to believe that survivals of such cults lurk in the dark corners of the world today.” - "The Children of the Night"
“As Xuthltan died,” continued the old Bedouin, “he cursed the stone whose magic had not saved him, and he shrieked aloud the fearful words which undid the spell he had put upon the demon in the cavern, and set the monster free. And crying out on the forgotten gods, Cthulhu and Koth and Yog-Sothoth, and all the pre-Adamite Dwellers in the black cities under the sea and the caverns of the earth, he called upon them to take back that which was theirs, and with his dying breath pronounced doom on the false king, and that doom was that the king should sit on his throne holding in his hand the Fire of Asshurbanipal until the thunder of Judgment Day. - "The Fire of Asshurbanipal"
"Let them forget the false teachings of Confucius and Buddha, and the gods of Tibet, who had allowed their people to come under the yoke of the white-skinned devils. Let them rise under the leadership of the prophet the Old Ones had sent them and the great Cthulhu would sweep them all to victory." - "Black John's Vengeance" "Mitra would have folks stand upright before him-not crawling on their bellies like worms, or spilling blood of animals all over his altars." -The Black Colossus, Robert E. Howard
Mithra is a member of the trinity of ahuras, protectors of asha/arta, "truth" or "[that which is] right". Mithra's standard appellation is "of wide pastures" suggesting omnipresence. Mithra is "truth-speaking, ... with a thousand ears, ... with ten thousand eyes, high, with full knowledge, strong, sleepless, and ever awake." (Yasht 10.7). Note: This is very Lovecraftian as well.
The celebration of the birth of Mithra took place on December 25. Note that the four generally accepted Christian gospels give no date for the birth of Jesus Christ. Mithraist stories tell of Mithra being visited by shepherds after his birth. Mithra healed the sick and raised the dead. Mithraists worshipped on Sunday. Note that the Hebrew Ten Commandments direct one to worship on Saturday ("seventh day"), not Sunday. The celebration of the visit of wise men to the young Mithra took place on January 6.
Mithraism had seven sacraments. Mithraism also had a ritual meal in which people were invited to drink of Mithra's blood and eat of his flesh--with the flesh of Mithra represented by bread.
In the Mythos of Lovecraft
The Bull: Nyarlathotep has been worshipped under several guises in all parts of the world. One of its most infamous cults was among the Stygians, who called it "Nyarlat" and brought its worship to Egypt after the Cataclysm. Mithra is depicted defeating Nyarlat in his form of the Black Bull.
The Crawling Chaos was one of the greatest gods in the land of the Nile, where it was the ruler of the Underworld, the master of the night, and the patron of sorcerers. After many years, however, the people of Egypt grew frightened of the dark god and struck out all references to it from their records and monuments, reassigning its attributes to other gods such as Set and Thoth. Though the enemies of the cult were able to suppress the memory of Nyarlathotep, a few remembered. Resurgences of its worship occurred throughout Egyptian history, the most famous of which were led by Nephren-Ka, the Hyksos, Nophru-Ka, and Nitocris. (It was during Nephren-Ka's reign that the suffix "-hotep", meaning "the gratified" was added to the god's name.) The Black Bull (Egypt) In the form of a bull or a human, Nyarlathotep will become the herald of the End Times in this guise. The heads of the cult are mummies who share a special hated with the Brotherhood of the Black Pharaoh.