Unlike many of her painter colleagues at the time, Ms. Frankenthaler, born in New York City on Dec. 12, 1928, came from a prosperous Manhattan family. She was one of three daughters of Alfred Frankenthaler, a New York State Supreme Court judge, and the former Martha Lowenstein, an immigrant from Germany. Helen, their youngest, was interested in art from early childhood, when she would dribble nail polish into a sink full of water to watch the color flow.

After graduation from the Dalton School, where she studied art with the Mexican painter Rufino Tamayo, she entered Bennington College in 1946. There the painter Paul Feeley, a thoroughgoing taskmaster, taught her “everything I know about Cubism,” she said. The intellectual atmosphere at Bennington was heady, with instructors like Kenneth Burke, Erich Fromm and Ralph Ellison setting the pace.

As a self-described “saddle-shoed girl a year out of Bennington,” Ms. Frankenthaler made her way into the burgeoning New York art world with a boost from Mr. Greenberg, whom she met in 1950 and with whom she had a five-year relationship. Through him she met crucial players like David Smith, Jackson Pollock, Willem and Elaine de Kooning and Franz Kline.

In 1951, with Mr. Greenberg’s prompting, she joined the new Tibor de Nagy gallery, run by the ebullient aesthete John B. Myers, and had her first solo show there that year. She spent summers visiting museums in Europe, pursuing an interest in quattrocento and old master painting.

Her marriage to Mr. Motherwell in 1958 gave the couple an art-world aura. Like her, he came from a well-to-do family, and “the golden couple,” as they were known in the cash-poor and backbiting art world of the time, spent several leisurely months honeymooning in Spain and France.

In Manhattan, they removed themselves from the downtown scene and established themselves in a house on East 94th Street, where they developed a reputation for lavish entertaining. The British sculptor Anthony Caro recalled a dinner party they gave for him and his wife on their first trip to New York, in 1959. It was attended by some 100 guests, and he was seated between David Smith and the actress Hedy Lamarr.