Mitra is a deity from the Hyborian Age setting created by Robert E. Howard for his Conan the Barbarian series of stories. Mitra is a personification of good popular among the Hyborian peoples.
He is probably loosely based on the Vedic and Zoroastrian figure by the same name, and in the Hyborian universe, his worship generally represents Christianity. In the essay "The Hyborian Age", Howard notes that followers of Mitra are urged to forgive their enemies (though many of them fail to actually do so - like many actual Christians, past and present). The Mitra religion is strongly missionary, its adherents sometimes risking their life in trying to spread it in hostile environments.
Significantly, Mitra worship is strong and dominant - effectively the state religion - in the Hyborian countries corresponding to Western Europe. In other parts of the world, corresponding to Asia and Africa, Mitra is at best one god among many, and in Stygia (Egypt/North Africa) worship of Mitra is altogether banned.
Mitra is the chief god of most of the civilized Hyborian kingdoms, including Aquilonia, Ophir, Nemedia, Brythunia, Corinthia, and Zingara. His worshippers are monolatristic, since at least one tale depicts priests of Mitra recognizing the existence of another deity (Set). He is depicted as a "gentle" god. In Khoraja, which is on the border line of the Hyborian kingdoms with the Semite ones, the worship of Mitra was largely forgotten in favor of the Semite gods - but in hours of great need, Khorajans still call on Mitra and are answered ("Black Colossus").
While Mitra and his followers are in general presented favorably in the Conan stories, in The Hour of the Dragon there is a considerable reference to Mitra followers having a strong prejudice against those of Asura and engaging in active persecution of them. Conan, being a "Barbarian", does not share this "civilized" prejudice and protects the Asura followers - which proves of great benefit in his hour of need.
The Mitran cult does not practice sacrifice and values aesthetic simplicity. Thus his shrines are usually unadorned and feature little or no iconography except for a single idol. The idol itself has the appearance of an idealized, bearded male figure and is the primary direction of Mitran worship. However, being omnipresent and incorporeal, Mitra is not considered to reside in the icon, nor share its appearance. He is also symbolically represented by a phoenix in Howard's writing, by an Ankh in the Age of Conan MMORPG, and by a bronze colossus in the survival video game Conan Exiles.
Mitra appears directly in "Black Colossus", where he speaks to Princess Yasmela of Khoraja and helps her at her hour of desperate need. Mitra's involvement has a significant effect on Conan's career. Due to the god's involvement Conan - who hitherto had never commanded more than a "company of cut-throats - gets the chance to become a general and emerge victorious from a major battle involving tens of thousands of soldiers and effecting the future of the whole world. Though Conan's career would known many more ups and downs, this was an important step towards his eventually becoming a King - for which he could thank Mitra. From Mitra's point of view, the god evidently considered Conan as the fighter best fitted to fight and defeat a sworn enemy of the Hyborian kingdoms, who had a ancient grudge against Hyborians and who intended to lead his armies to conquer and devastate the Hyborian kingdoms, the center of Mitra worship.
Mitra, along with Crom, is mentioned in the cartoon Conan the Adventurer. There he is the god of Jezmine, Conan's love interest. She says, "By Mitra!" in times of danger.
Mitra is also mentioned by the pirate Valeria in the story Red Nails.