Dan O'Bannon, 63, the science fiction/horror film screenwriter who was best known for writing the blockbuster hit

Alien

and who also directed and wrote the zombie fest

The Return of the Living Dead

, died Thursday at a hospital in Santa Monica, Calif.

Mr. O'Bannon, whose credits include cowriting Blue Thunder and Total Recall, lost his 30-year battle with Crohn's disease, a chronic form of inflammatory bowel disease, his wife, Diane, said.

His career began with the low-budget 1974 sci-fi film Dark Star, a dark comedy directed by John Carpenter that began as a University of Southern California student project and was cowritten by Mr. O'Bannon and Carpenter from their original story.

From Dark Star, which tanked at the box office, Mr. O'Bannon went on to write the script for Alien, director Ridley Scott's 1979 sci-fi classic about a spaceship terrorized by an alien being. It was based on Mr. O'Bannon's and Ronald Shusett's story.

Mr. O'Bannon said in a 2003 interview that he modeled the alien after the life cycle of parasitic microorganisms.

"One review said that watching this movie was like turning over a rock and finding something disgusting. That was a pretty good description of what I was going after."

He made his directorial debut with The Return of the Living Dead, a 1985 genre parody that O'Bannon described as being "to horror movies what Airplane! was to disaster films." - Los Angeles Times