The concept of a magus takes its name from the priests of the Magian religion of the ancient Medes, who wielded considerable power and influence, until they were suppressed as a result of a revolt by the pretender Smerdis against Cambyses II.
Similarly, Julius Caesar's Commentaries on the Gallic War portrays druids as a learned priestly class and the keepers of customary law, with the power of executing judgments. These druids were a non-hereditary class that became druids by submitting to an extensive program of training.
They were believed to wield magical powers to influence the outcome of battles, and offered sacrifices, including human sacrifice, to achieve these goals.
In Dungeons & Dragons the two main types of magic are arcane magic and divine magic. A government headed by the disciples of divine magic is called a theocracy. In a magocracy, only those with skill and power in arcane magic (wizards learn arcane magic through study and practice, while sorcerers have the innate ability to use arcane magic) have a voice in government. Thus, power is limited to the few who have the education (and in such societies, wealth is often needed for an education), or magical heritage.
Typically, arcane magic users will have privileges, and the citizens will live in fear. Divine magic may be restricted, or limited to followers of the state religion. In the world of Mystara, the Principalities of Glantri have banned all divine magic users.
Ursula K. Le Guin's fictional world of Earthsea could be called a magocracy. In this world, a school of magic constitutes the closest thing to a central government of an archipelago of pre-industrial cultures.
Guy Gavriel Kay's Tigana is a novel that features a conflict between two nations governed by sorcerers, in a world deliberately designed to be reminiscent of Italy during the Renaissance.
In BioWare's game Dragon Age, the Tevinter Imperium is a magocracy, ruled by Imperial Archons and magisters.
Within the Dungeons & Dragons role-playing worlds, perhaps the most well-known magocracy is that of the government of Thay, an ambitious empire that is ruled by the Red Wizards in the Forgotten Realms setting. It is an enemy to many nations, including Aglarond, Mulhorand and Rashemen.
The city-state of Dalaran in the Warcraft Universe is ruled by a group of wizards called the Kirin Tor.
Two theocratic-magocracies (though not referred to by that term) have also appeared in the Star Wars Expanded Universe, where Emperor Palpatine, inspired by a similar scheme initiated by the Sith-descended "Sorcerers of Tund," intended to use his grasp of the Dark Side to personally rule over the galaxy, instead of having his control mediated through a bureaucracy and military. His initial prototype for this scheme (incomplete at the time of his death at the Battle of Endor) was the planet Byss and by the Sith Emperor (formed before the Great Galactic War).
In The Black Magician trilogy, the kingdom of Sachaka is ruled over by powerful magicians known as Ashaki, while almost everyone else is enslaved.
In the Harry Potter series by J.K. Rowling, the wizarding world in England, Bulgaria and various other countries is ruled by a democratic magocracy, in the form of the Ministry of Magic, where a Minister for Magic is elected by witches and wizards. There are various political departments; four Ministers for Magic are mentioned in the series, the last being Kingsley Shacklebolt, and the first being Cornelius Fudge.
In the Discworld novel Sourcery by Terry Pratchett, the wizards of Unseen University institute a magocracy in Ankh-Morpork when their power is temporarily amplified by the presence of a sourcerer, the eighth son of a wizard and a primordial source of magic. They are ousted when the sourcerer consigns himself to a pocket dimension.