Stock, who was diagnosed with colon and liver cancer a few weeks ago and developed pneumonia in recent days, died Monday night at a hospital in Sarasota, Fla., said Mark Lubell of Magnum Photos.
"His singular most iconic image would definitely be his James Dean walking down Times Square with a cigarette in his mouth, because James Dean became an icon of a generation and that image represented so much to that generation," said Lubell, director of Magnum, aphotographic cooperative that Stock joined in 1951.
A native New Yorker and a Navy veteran who became an apprentice to Life magazine photographer Gjon Mili in 1947, Stock entered a Life magazine contest for young photographers in 1951 and won first prize for a series on immigrants.
Invited by legendary photographer Robert Capa to become an associate member of Magnum, Stock had early assignments in Paris before he began shooting the Hollywood scene.
Stock didn't know Dean was an actor until he'd finished talking to him.
"It wasn't apparent in his appearance," he told the Sarasota Herald-Tribune in 2005. "He was not a neat dresser per se. He looked tired, but he was pleasant and interesting."
Stock went with Dean to a sneak preview of "East of Eden" in Santa Monica, but the actor stayed outside with his motorcycle while Stock watched the movie.
Overwhelmed by Dean's performance, Stock proposed doing a "visual biography" on Dean. "I knew this guy would take off," he recalled.
The famous Times Square photo of Dean was just part of Stock's photo essay that appeared in Life magazine in 1955.
Before traveling to New York, Stock and Dean stopped in Fairmount, Ind., where Dean had spent much of his early years on his aunt and uncle's nearby farm.
Among the many images Stock shot during their stay were Dean posing with a huge hog on the farm, walking down Main Street and -- eerily -- posing in a coffin in a funeral home casket showroom.
"There were about six major photographers that photographed Dean quite a bit," said David Loehr, curator of the James Dean Gallery in Fairmount. "The Dennis Stock photos are thought to be some of the best photos of Dean."
They also are the only professional shots of Dean taken in his hometown, Loehr said. The visit to Fairmount was Dean's last. He died in a car crash in Cholame, Calif., on Sept. 30, 1955.
"I liked him sometimes, but not all the time," Stock told the Sarasota newspaper. "But he was like family after a while. We really bonded in Indiana. Not in New York, where he was distracted a lot. He was an insomniac and didn't get a lot of sleep and was a pain in the ass to work with."
Stock's Dean photographs were published in the 2005 book "James Dean: Fifty Years Ago."
Described by a British journalist as "a pugnacious roustabout of a man" who could be both combative and charming, Stock told the London newspaper the Independent that Humphrey Bogart was his mentor in Hollywood.
"He came to me one day and said, 'Listen, I'm gonna make a movie with a kid I think you should know more about. She's called Audrey Hepburn.' He arranged for Paramount to show me ‘Roman Holiday.’ She was stunning. I rang Esquire and said, 'I've seen this terrific girl.' "
Hepburn was, he said, "an absolute sweetie. She was very un-Hollywood, which was the key to the whole thing. She wasn't glamorous. She didn't try to be glamorous."
In the late 1950s Stock trained his camera on the jazz scene, shooting legends including Louis Armstrong, Billie Holiday and Miles Davis for his book "Jazz Street." In the late 1960s, he shot pictures in hippie communes in Colorado, New Mexico and California.
He took a leave of absence from Magnum in 1968 to create Visual Objectives, a film production company, and shot several documentaries.
In the 1970s and '80s, he worked on color books that emphasized the beauty of nature. He turned to an exploration of modern architecture in large cities in the '90s and more recently focused mostly on the abstraction of flowers.
Stock, who was born in New York City on July 24, 1928, and grew up in the South Bronx, was the author of more than two dozen books, and his photographs have been acquired by museums around the world.
He remained a member of Magnum Photos until his death.
Stock once described his career by saying, "I have been privileged to view much of life through my cameras, making the journey an enlightened experience."
He is survived by his wife, author Susan Richards; his children, Rodney Stock, John Raymond and Christina Stock; a grandson; and five great-grandchildren.