William Peter Blatty, who died on January 12 aged 89, was best known as the author of The Exorcist (1971), a horror novel about demonic possession which he turned into an Oscar-winning screenplay two years later.
Directed by William Friedkin and produced by Blatty, The Exorcist still makes a cultural impact, with numerous spin-offs and, most recently, a television mini-series. But it is forever associated with disturbing scenes of possession, including 360-degree head spins, obscene blaspheming and the projectile vomiting of green slime by child actress Linda Blair, who played the possessed Regan.
Blatty was already a comic novelist and scriptwriter when his horror novel was published but the success of the book and film marked a turning point in his career. The novel sold 13 million copies in the US alone and he won the Academy Award for best adapted screenplay.
Later, however, he regretted having been typecast as a horror writer. "The sad truth is," he said, "that nobody wants me to write comedy."
The youngest child of Lebanese immigrants, Blatty was born on January 7, 1928, in New York. His father left home when he was six and his mother sold quince jelly on the streets of Manhattan. His childhood, he later recalled, was "comfortably destitute".
His mother was a devout Roman Catholic and William was educated at the Jesuit-run Brooklyn Preparatory School and Georgetown University, where he read English. In 1949, while he was at Georgetown, he heard the story of a case of demonic possession and exorcism of a boy from Maryland which would later inspire The Exorcist.
After receiving his master's degree in 1954, Blatty worked for the US Information Agency in Lebanon before a spell in public relations at the University of Southern California and Loyola University in Los Angeles. There he pretended to be the son of a Saudi prince, an experience he later described in an article for the Saturday Evening Post.
In 1961, Blatty appeared as a contestant on the television quiz show You Bet Your Life, hosted by Groucho Marx, and after he and a fellow contestant won $10,000 he left his day job to become a full-time writer. Three comic novels followed in swift succession: John Goldfarb, Please Come Home! (1963), I, Billy Shakespeare (1965) and Twinkle, Twinkle, "Killer" Kane (1966), although they were not commercially successful.
During this period he began to collaborate with director Blake Edwards and wrote scripts for him including the second instalment in the Pink Panther comedy series, A Shot in the Dark (1964). They also collaborated on What Did You Do in the War, Daddy? (1966) and Darling Lili (1970), a musical starring Julie Andrews and Rock Hudson.
The death of his mother and a renewed interest in his Catholicism drove Blatty in a new direction, and in the late 1960s he began work on The Exorcist. Despite its popularity, the book was not universally acclaimed. One critic excoriated it as "a pretentious, tasteless, abominably written, redundant pastiche of superficial theology, comic-book psychology, Grade C movie dialogue and Grade Z scatology".
The film version was so offensive and upsetting that there were reports of fainting, heart attacks and miscarriages among those who saw it. Some viewers reportedly sought psychiatric treatment after screenings. None the less, it broke box office records and was nominated for 10 Academy Awards, winning two.
Blatty was not involved in Exorcist II: The Heretic (1977), although he wrote and directed the third instalment in the franchise (1990). In 1980, he wrote the screenplay for The Ninth Configuration (based on his earlier novel, Twinkle, Twinkle, "Killer" Kane). Later books included Demons Five, Exorcists Nothing (1996), which drew on his experiences as a screenwriter.
Latterly Blatty became reconciled to the fact his name would forever be associated with The Exorcist, whatever else he chose to write. He was adamant, however, that the story was redemptive. The point of the film, Blatty said in 2000, is "that God exists and the universe itself will have a happy ending".
His fourth wife Julie, who he married in 1983, survives him, as do his several children.