Priest (Prince of Darkness)

The Priest is one of the main protagonists of the 1987 horror film, Prince of Darkness.

He learns of Satan's true nature and the Brotherhood of Sleep after the final member of the sect, Father Carlton, died of natural causes and left behind a key and a diary. Feeling Satan's power growing, the Priest hires Professor Howard Birack and his students and other academics to prove Satan's existence to the outside world.

As the film progresses, the Priest realizes the corruption of the church for hiding Satan's existence and true nature to bring his father, the Anti-God back from the dark side. When it's revealed that Jesus came to warn us about Satan and his father, the Priest finally accepts that the Catholic church were just "salesmen selling a product." During the time in the church, the group have a dream about a dark figure coming out of the church, caused by humans in the future using a Tachyon transmitter to influence the dreams of anyone near the canister. Satan starts to free itself from its corroded prison and slowly begins to possess the group as zombies.

Two of the zombies bring the canister to where one of the students, Kelly, was sleeping. The entirety of the liquid then rises to the ceiling and enters Kelly's body to make her his vessel. The zombies then attack the group while the priest is forced to hide. One of the zombies sees a large mirror where the priest was hiding and puts its hand on it in an attempt to free the Anti-God but without Satan's full power, it was a futile effort.

Satan then fully possesses Kelly, and attempts to use the mirror to free his father. The Priest grabs an axe and chops off one of Kelly's arms and decapitates her just as her arms regenerates. Kelly then grabs her head and the Priest starts praying. Kelly then uses psychokinesis and traps the Priest with a large object. Kelly attempts to free the Anti-God but one of the student, Catherine Danforth sacrifices herself by tackling Kelly and trapping both on the other side with the Anti-God. The Priest is then able to use the axe to shatter the mirror, defeating Satan and the Anti-God. Satan's defeat causes the zombies to die and Satan's influence in the world begins to wane.

Brian Marsh, who was in love with Catherine, dreams about the dark figure becoming Catherine. He rolls in bed and sees a disfigured Catherine next to him, waking him up from his nightmare. He walks to his mirror but the film ends before we find out what happens.

Trivia
The Priest was played by the late Donald Pleasence, who is famous for portraying Dr. Samuel Loomis in the Halloween movies.

Prince of Darkness was the second of what John Carpenter called his Apocalypse Trilogy, which started with his remake of The Thing and ended with In the Mouth of Madness.