Buffy Cafritz, a Washington philanthropist who served on the boards of cultural organizations, including the Kennedy Center and a support group for the Library of Congress, and was known for hosting star-studded gatherings of the city’s political and cultural elite, died May 4 at a Washington hospital. She was 91.

The cause was pneumonia, said her son, Charles “Sandy” Wilkes.

Mrs. Cafritz, one of the last of the District’s grand dame host­esses, threw quadrennial inaugural parties for nearly three decades. They became coveted affairs for many in the Washington establishment.

She and her husband, real estate developer William N. Cafritz, who were Republican supporters, organized their first inaugural gala in 1985, when President Ronald Reagan — whom they had entertained at their home — was entering his second term. In bipartisan fashion, the Cafritzes often shared hosting duties with prominent Democrats.

“We wanted to have a bipartisan gathering because the country seemed so divided,” Mrs. Cafritz told The Washington Post in 2017. “It was a great success, so together we said, ‘Let’s have this every four years.’ ”

The parties were held through 2001 at the Jockey Club in the Fairfax Hotel on Massachusetts Avenue NW and later at other hotels. Mrs. Cafritz pored over the guest list as if she were curating an art exhibition, inviting congressional leaders from both major parties, Supreme Court justices, State Department officials, celebrity journalists and a few select Hollywood stars.

In 1993, when President Bill Clinton was inaugurated, Mrs. Cafritz shared hosting duties with broadcaster Phyllis George, who was then married to a onetime Democratic governor of Kentucky. That year’s party included such luminaries as Warren Beatty, Annette Bening, Lauren Bacall, Jack Lemmon, Kathleen Turner, Chevy Chase, Shirley MacLaine, Robert De Niro, Penny Marshall, Barbara Walters and members of the Kennedy political family. Actor Jack Nicholson was still holding court at 3:45 a.m.

Millionaire party crashers without invitations were turned away at the door.

Believing that friendship and after-hours camaraderie should transcend political affiliation, Mrs. Cafritz cultivated relationships with first ladies Nancy Reagan and Hillary Clinton. In the 1990s, Mrs. Cafritz and her husband were joined as inaugural party hosts by Vernon and Ann Jordan, power brokers in Washington’s Democratic establishment. Their final inaugural party took place in 2013.

For 25 years, Ann Jordan and Mrs. Cafritz also co-chaired the annual dinner after the Kennedy Center Honors, for about 1,600 guests. This year’s Kennedy Center Honors, to be presented in a virtual ceremony later this month, will be dedicated to Mrs. Cafritz, a former member of the performing arts center’s board of trustees.

She also served on the boards or advisory committees of more than a dozen other charities and cultural organizations, including the National Gallery of Art, the James Madison Council of the Library of Congress, the Ronald Reagan Presidential Library, Ford’s Theatre, the National Institutes of Health Foundation, the White House Historical Association, the French-American Cultural Foundation and Sasha Bruce Youthwork, which seeks to reduce homelessness among children.

Mrs. Cafritz seldom granted interviews, and acquaintances said her philanthropy was often carried out without fanfare or public notice.

“She enjoyed making other people happy,” said CNN anchor and reporter Pamela Brown, a longtime friend of Mrs. Cafritz. “It was her way of giving.”

Brown, who is the daughter of George and former Kentucky governor John Y. Brown Jr., said Mrs. Cafritz became “a second mom for me” after she moved to Washington.

“She hosted my engagement party,” Brown said. “I was late for my own engagement party, but Buffy was there at the door, greeting every single guest.

Mrs. Cafritz was born Anita Marie Boffa in Westport, on Nov. 2, 1929. She grew up in Norwalk, Conn. Her father was chairman of a finance company, and her mother was a homemaker.

She acquired the nickname “Buffy” from her last name and was a 1947 graduate of the private Rosemary Hall (now Choate ­Rosemary Hall) in Wallingford, Conn. She graduated in 1949 from Colby Junior College (now Colby-Sawyer College) in New London, N.H.

She settled in Washington in the early 1950s. Her first marriage, to lawyer Charles L. Wilkes, ended in divorce. Her second husband, William Cafritz, a nephew of Washington business leaders and benefactors Morris and Gwendolyn Cafritz, died in 2014 after 55 years of marriage.

Survivors include a son from her first marriage, Charles “Sandy” Wilkes, who was adopted by William Cafritz, of Kensington, Md.; three granddaughters; and a great-granddaughter.

A daughter from her second marriage, Pamela Cafritz, died in 2016.

Mrs. Cafritz lived in Bethesda, Md., where she was a regular parishioner at Our Lady of Lourdes Catholic Church. In a brief interview with The Post in 1982, she described the diet followed by women in Washington society.

“I don’t think anyone can eat and stay thin,” she said. At parties, her favorite cocktail was water with a twist of lemon.