Exorcism
In Christianity, exorcism is the practice of casting out demons. In Christian practice the person performing the exorcism, known as an exorcist, is often a member of the Christian Church, or an individual thought to be graced with special powers or skills. The exorcist may use prayers and religious material, such as set formulas, gestures, symbols, icons, amulets, etc. The exorcist often invokes God, Jesus and/or several different angels and archangels to intervene with the exorcism. Protestant Christian exorcists most commonly believe the authority given to them by the Father, Son, and Holy Spirit (the Trinity) is the source of their ability to cast out demons.
The Exorcist
In "Angel: Earthly Possessions", a spin-off comic story based on the TV series "Angel", protagonist Angel finds himself dealing with a priest who performs exorcisms, but comes to realize that the priest is summoning the demons for him to exorcise in the first place. He also makes a note of "The Exorcist" film, noting that the vision it created of possession actually made things easier for possession demons by making it harder for humans to know what to expect from a possession.