Father Sean O’Malley is a Catholic priest and one of the protagonists of the Utgarda Trilogy. From The Old Man’s Request: Book One of the Utgarda Trilogy, we learn that:

“Sean O’Malley was not a typical parish priest. He was a Professor of Ancient History specializing in the Dark Ages. His training had been under the tutelage of Father Christophé, the exorcist from Martinique regarded as the Church’s leading “expert” on the activities various “nameless cults.”

Excerpt From: Stieglitz, Joab. “The Old Man’s Request: Book One of the Utgarda Trilogy.” Lulu.com, 2016-12-01. iBooks. 

In The Missing Medium: Book Two of the Utgarda Trilogy, we learn that O’Malley is a member of the secret Vatican Order of Saint Dionysius the Aeropagite, patron saint of protection from the devil.

Sean O’Malley was another player character from a Call of Cthulhu RPG campaign that I ran in the 1990’s, though the original Father O’Malley was just a regular parish priest.