Marion O. Sandler, a billionaire philanthropist who made her fortune in the savings and loan industry and whose business dealings were scrutinized in the wake of the 2008 mortgage crisis, died June 1 at her home in San Francisco. She was 81.

The death was announced by her family. No cause of death was provided.

For more than 40 years, Mrs. Sandler was the co-chief executive of Golden West Financial with her husband, Herbert Sandler. The couple had a seamless partnership and led their firm through prosperity and growth, turning a small savings and loan operation in California into a financial juggernaut with $124 billion in assets.

“You know that old saying about it being lonely at the top?” Herbert Sandler told the New York Times in 1990, discussing his partnership with Mrs. Sandler. “Well, it’s not here.”

Along the way, the Sandlers became billionaires known for their generosity. They championed liberal causes and gave millions of dollars to Human Rights Watch and the American Civil Liberties Union.

Marion O. Sandler, who was co-chief executive of Golden West Financial with her husband, Herbert Sandler, died June 1 at 81. (Marcio Jose Sanchez/AP)

With John Podesta, a former chief of staff in the Clinton White House, they helped found the Center for American Progress, a Washington-based think tank. In 2008, they provided funding to start ProPublica, a nonprofit investigative journalism organization.

Recently, ProPublica has collaborated on news stories with The Washington Post and the New York Times. In partnership with the Times, ProPublica won a 2010 Pulitzer Prize for a report on the dire conditions at a New Orleans hospital during Hurricane Katrina.

Through an initiative started by Bill Gates and Warren Buffett, the Sandlers pledged to give away the majority of their wealth to charitable groups.

The couple met one summer in the Hamptons. She was a Wall Street securities analyst; he was a corporate lawyer. They married in 1961.

Two years later, they purchased a Northern California savings and loan company for $3.8 million and ran the business jointly. They regarded their outfit as a mom-and-pop operation, and Mrs. Sandler was said to have knitted sweaters and scarves during business meetings.

Through careful stewardship — the Sandlers were known for their aversion to risk — Golden West Financial steadily became more prosperous.

(The Sandlers were so conservative that they agreed to install automated teller machines only in the 1990s. They said they had feared the devices would not be worth the investment.)

The vast majority of the loans offered through their World Savings Bank subsidiaries were residential mortgages for single-family homes. It has been reported that the Sandlers helped popularize a form of adjustable rate mortgages known as option ARMs.

The “Pick-A-Pay” mortgages, as the financial tools were called, allowed borrowers to choose how much of their loans to pay off each month. In many cases, unpaid interest was added to the balance. That unsustainable arrangement forced many borrowers to default on their mortgages.

In 2006, Golden West Financial was sold to Wachovia for $25 billion. Mrs. Sandler and her husband earned $2.4 billion in the deal.

Two years later, the housing market collapsed. Defaulted Pick-A-Pay mortgages were said to have contributed to the financial meltdown. Wachovia posted tremendous losses stemming from its residential loans branch and nearly collapsed. It was sold to Wells Fargo in 2008.

Christopher Whalen of the Institutional Risk Analytics group once described Golden West Financial in a report as “the poster child for the U.S. real estate bubble.”

Marion Anna Osher was born Oct. 17, 1930, in Biddeford, Maine. Her parents were Lithuanian and Russian immigrants who ran a plumbing supply and hardware store. The family also invested in real estate.

Mrs. Sandler was a 1952 graduate of Wellesley College in Massachusetts and received a master’s degree in business administration from New York University in 1958.

Survivors include her husband of 51 years; two children; two brothers; and two grandchildren.