Thomas died of natural causes Sunday at his Sherman Oaks home, his son Pete told the Times ( http://lat.ms/1ldVFp2). He was 89.
Thomas led the Times from 1971 to 1989, when the newspaper widened its reach with the opening of domestic and foreign bureaus while launching a Sunday magazine, Book Review and regional editions.
Previously, when Thomas was metro editor, the newspaper won its first Pulitzer for local reporting for its coverage of the 1965 Watts riot.
"He was perhaps the least well-known of any editor of any major newspaper," said Tom Johnson, who previously served as Times publisher and president of CNN. "He never sought the spotlight for himself. His passion was for great writing."
Thomas established the newspaper's reputation for literary journalism by giving reporters the freedom to pursue more esoteric stories that didn't usually appear in newspapers.
Thomas fulfilled Publisher Otis Chandler's ambition of putting the Times on the level of its more established rivals, the New York Times and Washington Post.
Along with breaking news and investigative reports, "there were a couple of stories in the paper every day that you might have found .
During his nearly three decades at the Times, Thomas saw a rise in circulation from 757,000 daily subscribers in 1962 to more than 1.1 million in 1989, when he retired.
Thomas, a Michigan native, was a World War II veteran who earned degrees in journalism from Northwestern University.
His wife, Pat, whom he married in 1948, died in 2000. He is survived by sons Michael, Peter and Scott and a granddaughter, Kasey.
Information from: Los Angeles Times, http://www.latimes.com