Paramedics summoned to his home by a housekeeper pronounced him dead at 12:40 p.m., said Ed Winter, assistant chief of investigations for the Los Angeles County coroner's office.
An official cause of death will be determined after an autopsy and toxicology tests, but Winter said possible causes include a drug overdose. He said Ring appeared to have undergone recent surgery and medications were found in the home.
Ring was married to former Los Angeles City Councilwoman Cindy Miscikowski, who returned from China on Friday after being notified of his death. She was overseas on official business as president of the Los Angeles Harbor Commission.
A longtime former lobbyist and well-connected political donor who mainly supported Democratic candidates, Ring was well known in city and county government.
He founded the Ring Group, a real estate investment firm, and sat on a number of public boards. His civic posts included serving as president of the city Board of Library Commissioners and Los Angeles Children's Museum and as a member of the city Community Redevelopment Agency.
A lover of modern art, he also was a longtime trustee of the Museum of Contemporary Art, where he helped fund several shows, including the Andy Warhol retrospective in 2002.
"He was a fixture in Los Angeles . . . in business, the arts, public policy and in the nonprofit world," said Los Angeles County Supervisor Zev Yaroslavsky, who knew Ring for 40 years. "His death is a real loss to Los Angeles. He was one of those people who made such a difference in so many arenas."
Ring also was executive director of USC's Selden Ring Award, a $35,000 annual prize for investigative journalism named for his father, a prominent Los Angeles builder of apartments who passed on extensive holdings in Marina del Rey to his son when he died in 1992.
Douglas Ring's dealings in Marina del Rey often sparked controversy. In 2000, the Board of Supervisors approved without competitive bidding 39-year lease extensions on prime waterfront property controlled by Ring, who was a major campaign donor to most of the supervisors then on the board. Real estate experts said the lease agreements would pay the county unusually low rates for such desirable waterfront parcels.
Until the mid-1990s, one of Ring's partners in the marina leases was former Democratic state Sen. Alan Robbins, who served 20 months in prison after pleading guilty to federal corruption charges for extorting payments from lobbyists and former business partners. Ring told The Times in 2000 that Robbins was severed from the partnership as part of the settlement of a civil dispute.
Supervisor Don Knabe, whose district includes the marina, called Ring "a visionary" for his work in upgrading the marina. He said Ring was a strong advocate for incorporating low- and moderate-income housing in marina projects. "He was one of the first to force that issue to a head," Knabe said.
Ring was born July 24, 1944, in Rochester, N.Y., and grew up in Los Angeles.
He lived on a kibbutz in Israel in 1967 and underwent rabbinical training in Jerusalem and at Hebrew Union College in Los Angeles, but never was ordained. He earned a bachelor's degree in political science at La Verne College in 1973 and a law degree at the University of West Los Angeles in 1977.
Ring gained government experience in the late 1970s working for Supervisor Baxter Ward. During the 1980s and '90s, he was a lobbyist for corporate clients with major real estate projects needing local government approval.
He gave up that practice in 1996 when Miscikowski, whom he married in 1988, was elected to the City Council, representing parts of the Westside and San Fernando Valley.
In 1999, she abstained from the City Council's 9-3 vote approving Ring's appointment to the Community Redevelopment Agency board. His appointment by Mayor Richard Riordan had stirred complaints of cronyism and conflict of interest.
Antonia Hernandez, president of the California Community Foundation, said Ring was "quiet as a philanthropist" but gave generously to a wide array of causes, particularly scholarships and programs benefiting inner-city children.
One of his more visible causes was the Los Angeles Central Library. An avid book collector since his youth, he was a "driving force that kept the campaign together," said Yaroslavsky, who was a Los Angeles city councilman during the six-year effort to renovate and expand the library after two arson fires in 1986.
As president of the library board in 1993, Ring was instrumental in planning and implementing a public relations campaign aimed at building excitement about the city library system and the reopening of its main facility.
In addition to his wife, Ring is survived by a brother, Grant; a sister, Karen Lawrence; an aunt; and an uncle.
Funeral services will be at 11 a.m. Tuesday at Hillside Memorial Park, 6001 Centinela Ave., Los Angeles.
Memorial donations may be made to the American Civil Liberties Union of Southern California, the California Community Foundation or other charitable groups.