Gray and his wife, Marie, started the company in a San Fernando Valley garage in 1962 on a romantic whim. Marie Hermann, a model who used the surname St. John professionally, wanted to raise money for a Hawaiian honeymoon, the story goes. She persuaded her fiance, Gray, who was an apparel salesman, to show a sample of a dress she designed and knit to a store buyer, thinking she might sell 20. Gray returned with orders for almost 200.
The couple married later that year, having almost accidentally launched a business that would grow into a global luxury brand.
Gray was born in Minnesota in 1925, but moved early in life to Southern California, where his father worked on movie special effects and his mother was a homemaker.
Gray earned a bachelor's degree at USC and intended to go to law school until a summer job with a friend's father lured him into the apparel business, his wife said.
The couple's fledgling enterprise did $92,000 in sales its first year, and by the early 1970s annual sales topped $1 million. In 1972, the Grays moved the company from Los Angeles to Irvine.
"We did every aspect of the work," Robert Gray recalled in a 2000 interview with The Times. "I used to be the shipping clerk, while she ran the factories; I did the selling, she did the designing. It was very easy for us to be very hands-on.
"I could certainly over the years be accused of overmanaging," he said. "But that's just the way I've managed the business."
The knit suits, dresses and sportswear meticulously made from the wool of Australian sheep were noted for their quality and Chanel-like timelessness. They were worn by lawyers, businesswomen and top movers and shakers, such as Hillary Rodham Clinton and Madeleine Albright.
The company's annual warehouse sale in Orange County drew women by the hundreds, some camping out overnight for the chance to restock their closets at 70% off.
In 1989, the Grays sold a controlling interest in the firm to German luxury brand Escada AG. In 1993, Escada took it public, with Robert Gray remaining as chairman and chief executive.
In 1999, the Grays and Vestar Capital Partners, a private equity firm, bought up all the shares and took the company private again, with Vestar holding the controlling interest.
When Gray retired in 2002, St. John had grown from a two-person enterprise to an international label with 4,800 employees and $365 million in annual sales.
Marie Gray and the couple's daughter, Kelly Gray — who had worked at the firm since she was 12, rising to become co-president and creative director and serving as the line's longtime model — ended their day-to-day roles in 2005.
"I'm very proud of the people he touched," Marie Gray said. "And of the company he built and the family he loved."
Besides his wife and daughter, Gray is survived by two sons from a previous marriage, Michael and Guy Gray; six grandchildren; and two great-grandchildren. Services will be private.