Pazuzu

“	Your mother sucks c-cks in Hell!	„
	~ Pazuzu taunting Father Damien Karras

Pazuzu is the main antagonist of The Exorcist. He is an ancient demon who possesses 12-year-old Regan Macneil, turning her into a hideous vessel for it to mercilessly taunt and abuse those around itself while also displaying supernatural powers that increased as the story progressed. It presumably grew in strength as the demon took more and more control over Regan's body - which twisted her into a demon of herself which included behaviors. Regan's mother became desperate and sought two priests, Damien Karras and Lancaster Merrin, to exorcise the demon from her daughter after several failed attempts to solve the problem by more scientific methods (with Regan violently attacking doctors and therapists). That proved trickier than expected as even the priests were reluctant to perform an exorcism due to the belief that such things were confined to the Dark Ages.

The two priests struggled to contain the vast powers of the creature. Sadly, the battle proved too much for Merrin, who died of a heart attack during the exorcism. Karras became enraged when Pazuzu mockingly laughs at his futile attempts to revive Merrin while demanding him and was possessed by the demon after forcing it out of Regan through physical force upon which the priest leapt out of the window to his death. Pazuzu dispersed when the two priests died.

Pazuzu discovers the soul of an executed serial killer known as the Gemini Killer, and he transfers it into Karras' broken body thus contributing to the Gemini Killer's killing spree. He again possesses Karras after The Gemini lost control in possessing the old woman dressed as a nurse, and failed to murder Kinderman and his family by the arrival of Father Morning in an attempt to perform an exorcism on the patient. Pazuzu severely wounded and mutilated Morning in response for interrupting the Gemini's killing spree, and Kinderman arrives in time to euthanize Karras after finding the body of the priest, only to be hurled into the wall and later in the ceiling by the possessed Karras. Pazuzu along with the Gemini, was dispersed once more after Morning manages to bring Karras back to his senses and briefly regains control of his free will to receive a mercy kill from Kinderman to free him from the demons control.