Christians...first called that in Antioch.
The fans of messi are called the Messiahs, from the name Messi.
The Six Messiahs was created in 1995.
The followers of Hinduism are called Hindus
Followers of god Shiva are called Shaivites.
Mussolini's fascist followers were called "Blackshirts."
Jesus
The followers of John Calvin were actually called Puritans.
Hazrat Isa AS is called Jesus Christ. His followers are called the Christians.
John Calvin's followers were called Huguenots in France.
They are called "Satanist" If they are followers of Satan, then they are generally called Satan or devil worshipers. If they are followers of satanism which is different then they are refered to as a satanist.
The Mirthful Messiahs are the being that Gamzee and Kurloz Makara along the other subjuggulators (a fictional alien religion) in the popular internet webcomic, Homestuck, By Andrew Hussie. It is later revealed that the Mirthful Messiahs are Violent J and Shaggy 2 Dope, of the band Insane Clown Posse. Angered, Gamzee goes on to believe that he himself is both of the messiahs.
If you are referring to Francis of Assisi, his followers are called Franciscan. If you refer to St. Francis Xavier, his followers are called Jesuits.