Herbert Vogel, a retired New York postal worker who, with his wife, Dorothy, created one of the world’s most unlikely — and most significant — collections of modern art, then bequeathed much of it to the National Gallery of Art, died July 22 at a nursing home in New York City. He was 89.

His death was confirmed by Anabeth Guthrie, a spokeswoman for the National Gallery of Art. The cause of death was not immediately disclosed.

In 1962, when Mr. Vogel and Dorothy Hoffman were married, they came to Washington on their honeymoon and spent several days visiting the National Gallery and other museums. When they returned to New York, they began to buy a few pieces by artists they met, slowly amassing their collection.

Unlike many collectors, the Vogels were not wealthy people. They lived and collected their entire lives on their salaries and their pensions. Mr. Vogel worked nights sorting mail at New York post offices, and his wife was a reference librarian in Brooklyn.

The Vogels never talked about how much they paid for a work of art and did not sell a single piece they owned until the National Gallery acquired much of their collection in 1991. By then, its value was estimated to be well into the millions.

Herbert and Dorothy Vogel at the University of Michigan in 1978, from “Herb & Dorothy,” an Arthouse Films release, 2009. (Cecil Lockard)

“We could have easily become millionaires,” Mr. Vogel told the Associated Press in 1992. “We could have sold things and lived in Nice and still had some left over. But we weren’t concerned about that aspect.”

When they began collecting in the early 1960s, the Vogels — known to many in the art world simply as “Herb and Dorothy” — concentrated largely on conceptual art and minimalism. It was difficult, edgy work, often with straight lines and little ornamentation, that stood apart from the better-known abstract expressionist and pop art movements.

Their first purchase was “Crushed Car Piece” by John Chamberlain, who made sculptures from wrecked auto parts. It was not the sort of art that was in strong demand.

The Vogels visited studios and became close friends with many artists, including Sol LeWitt, Richard Tuttle and the husband-and-wife duo of Christo and Jeanne-Claude. They were often the first collectors to open their wallets to buy from unknown artists. Over a period of almost 50 years, the Vogels amassed more than 5,000 works of art, including drawings, paintings, sculptures and pieces that defied classification.

“Many millionaire collectors wouldn’t have the nerve to buy the kind of cutting-edge art that the Vogels embraced enthusiastically,” Philadelphia Inquirer art critic Edward J. Sozanski wrote in 1994. The Vogels, Sozanski continued, created “one of the most remarkable American art collections formed in [the 20th] century, one that covers most of the important developments in contemporary art.”

Herb and Dorothy Vogel had three requirements in purchasing art: It had to be inexpensive; it had to be small enough to be carried on the subway or in a taxi; and it had to fit inside their one-bedroom apartment. Over time, the diminutive couple – neither of them much taller than 5 feet – became recognized in the art world.They haunted the galleries and studios of New York, attending as many as 25 art events a week. They studied art magazines and kept in close touch with dozens of artists.

“They did not have deep pockets,” Earl A. Powell III, director of the National Gallery of Art, said in an interview. “They did not collect work by marquee artists at the time, but many of them later became well known.”

What began on a whim built on small purchases grew into a deep and wide-ranging collection that included many of the leading artists of the past 50 years: Chuck Close, Donald Judd, Robert Mangold, Dan Flavin, Joseph Beuys, Brice Marden, Nam June Paik, Edda Renouf, Edward Ruscha, Robert Ryman, Julian Schnabel, Robert Smithson, Carl Andre, Lynda Benglis, John Baldessari and Jeff Koons.

“We never bought anything because we thought it was important,” Mr. Vogel told the New York Times in 1992. “We bought things we liked. It’s not about price. It’s about feeling.”

The Vogels acted on intuition and personal taste, trusting their instincts rather than the advice of high-priced consultants or galleries. They bargained directly with the artists, sometimes buying on installment, paying as little as $10 a month. Once, they received a collage from Christo in exchange for cat-sitting.

Pat Steir, whose paintings often resemble waterfalls, met the Vogels through LeWitt, an artist noted for his geometric paintings and sculptures.

“When they first bought from me, I called Sol and said, ‘What should I charge them?’ ” Steir told W magazine in 2008. “And he said, ‘Take off three zeros and cut the price in half.’ And then they paid month by month on the installment plan.”

Artists considered it a privilege to be included in the Vogel Collection and an even greater honor to be invited to the couple’s cramped apartment for a meal. Dorothy Vogel would sometimes offer a TV dinner that she warmed up in the oven.

Their small apartment was quickly overrun with art, which hung on the walls and was stacked on the floor and under the bed. They got rid of their sofa and had only enough room to sleep, eat and care for their cats – as many as eight at a time – and the exotic turtles and fish that Mr. Vogel kept in aquariums.

“They were a couple without children,” said Ruth Fine, a recently retired curator at the National Gallery who has worked with the Vogels since 1987. “The works of art became the absolute focus of their lives.”

When Mr. Vogel retired from the Postal Service in 1979, he used his pension to buy more art. He and Dorothy began to think about the legacy they wanted to leave the world, and many top museums came calling.

On their 25th wedding anniversary in 1987, the Vogels paid a return visit to the National Gallery, where their love affair with art – and with each other – had blossomed.

Jack Cowart, the National Gallery’s curator of 20th century art at the time, met the Vogels and visited their home in New York.

“It was a very small apartment,” he recently recalled. “It was particularly dark, and it was particularly crammed full of packing crates, folders, artworks and books. Artworks were hanging from the ceiling, and I would hit my head against them. It had turtles and cats. It was astonishing. The collection had taken over the apartment.”

After years of negotiations with Cowart and then-director J. Carter Brown, the Vogels agreed to send the heart of their collection to the National Gallery. The terms have never been disclosed, but the deal included both purchases (on the part of the National Gallery) and gifts (from the Vogels).

“We wanted to do something for the nation,” Mr. Vogel told the Houston Chronicle in 1992. “The National Gallery doesn’t sell works they acquire. They’ll keep the collection together. And they don’t charge admission.”

When curators began to catalogue the collection, it took five full-size moving trucks to transport the Vogels’ art to Washington from their apartment.

“This was a fabled collection,” said Cowart, who is now executive director of the Roy Lichtenstein Foundation. “We all knew the National Gallery would never be able to acquire, piece by piece, such an astonishing collection.”

The National Gallery’s Vogel Collection now contains more than 900 works, and almost 300 more have been promised to the museum. The National Gallery staged major exhibitions drawn from the collection in 1994 and 2001.

“Their collection was lovingly formed in a very personal way,” said Powell, the National Gallery director. “They weren’t collecting for the National Gallery of Art. They were collecting for themselves and for an apartment in New York.”

Herbert Vogel was born Aug. 16, 1922, in New York City. His father was a tailor, and he grew up mostly in Harlem. He never completed high school.

After serving in the Army during World War II, Mr. Vogel began working as a postal clerk, sorting mail at various post offices throughout Manhattan. He worked mostly at night, which allowed him to study art history at New York University during the daytime. He never told his coworkers about his interest in art.

He married Dorothy Hoffman in 1962. Besides his wife, survivors include a sister.

The Vogels took painting classes and had a studio for several years, with the hope of developing careers as abstract expressionists. They gave up their studio when they realized that were more interested in other artists’ work than in their own.

They lived simply, eating at neighborhood diners and Chinese restaurants. They stopped traveling to Europe in the 1970s in order to have more money to spend on art. They usually paid cash or worked out novel arrangements with artists.

“When they came to the studio, they always came with a wad of cash,” the renowned painter Chuck Close said in a 1992 interview with the New York newspaper Newsday. “You’d always wind up selling something for a fraction of what it was worth.”

The Vogels were featured on “60 Minutes” and in a 2008 documentary film by Megumi Sasaki called “Herb and Dorothy.” Their names have been carved in the wall at the entrance to the National Gallery’s West Building alongside those of other major benefactors.

After the National Gallery moved out about 2,500 pieces from the Vogels’ apartment in 1990, they filled it with more art over the next 20 years.

Mr. Vogel could not always articulate why he liked certain works of art more than others or what he looked for when collecting. Sasaki, the director of the 2008 documentary about the Vogels, ended up focusing the camera on his eyes, which instantly grew wide whenever he saw a new artwork that he admired.

“I just like art,” Mr. Vogel said in 1992. “ I don’t know why I like art. I don’t know why I like nature. I don’t know why I like animals. I don’t know why I even like myself.”