After eventually breaking into movies with The Duellists in 1977, he began work on Alien, a chilling 1979 sci-fi which pitted the crew of a mining spaceship against a sleek, murderous creature designed by HR Giger.
He said: "I'd never been a sci-fi buff until I saw Stanley Kubrick's 2001, and that was just amazing. And George Lucas' Star Wars was seminal. I couldn't speak for a week. I sat there and thought, 'What have I been doing?'."
While Ridley admits "nothing happens for the first 45 minutes" in his own masterwork, Alien birthed one of sci-fi's most memorable moments when a tiny hissing creature exploded out of a crew member's chest over dinner.
Ridley said: "From all those years of commercials, I knew I was going to use blood, KY Jelly and back light and all the segments were going to work out.
"I kept the monster away from all the actors. There was so much blood on the set that you had to do a take, wrap and come back in a week when it had all been cleaned up with alcohol.
"Roger [Christian - production designer] came in with the little demon in a shopping bag. We had an artificial chest screwed to the table. John [Hurt] was underneath, so it was an illusion that his neck was attached to that body.
"I had to cut through the chest with a razor blade as it wouldn't burst. And when it happened there was total silence. I think Yaphet [Kotto, who played Parker] started to shriek with laughter. We never went back. It was one take.
"People were saying the footage was gross and I didn't know whether that was a compliment or not. One of the studio guys had his daughter in watching the rushes and she was nine. He said it was over the top, and I said, 'You pay me for this. We're doing a film that's completely over the top'."
The grotesquely beautiful design of Alien still petrifies and captivates audiences thirty years later. But Ridley is preparing for the next leap in cinema technology.
He said: "I'm filming a book by Joe Haldeman called Forever War. I've got a good writer doing it. I've seen some of James Cameron's work, and I've got to go 3D. It's going to be phenomenal."http://www.wharf.co.uk/2009/03/ridley-scott-on-alien-3d-and-s.html