Eugene V. Thaw, a major American collector of European old master art and one of the world’s most respected dealers in the field, died on Wednesday January 3 2018 at his home in Cherry Valley, N.Y. He was 90. His death was confirmed by Katie Flanagan, president of a charitable trust established by Mr. Thaw and his wife, Clare E. Thaw, who shared his art-collecting enthusiasms. He was born on Oct. 27, 1927, in Washington Heights in Manhattan. His father was a heating contractor, his mother a schoolteacher. They named him for the socialist leader Eugene Victor Debs, who had died the previous year. Mr. Thaw took drawing classes at the Art Students League on West 57th Street in Manhattan. But he did not pursue the hands-on practice of art. After graduating from DeWitt Clinton High School in the Bronx at 15, he entered St. John’s College in Annapolis, Md., and began making day trips to art museums in nearby Washington. Returning to New York in 1947, he took graduate classes in art history at Columbia University with Millard Meiss and Meyer Schapiro. In 1950, with a loan from his father, he opened a gallery above the Oak Room of the Algonquin Hotel on West 44th Street. In 1954, he moved to Madison Avenue, where he shared a floor with a carpet dealer and a beauty salon. That same year he married Clare Eddy, his gallery assistant. His closest institutional tie was to what is now the Morgan Library and Museum, which in the 1950s was one of the few New York museums to have a curator of drawings. In 1975, after the museum had expanded its acquisition parameters to include 19th-century work, the Thaws decided that the Morgan would be the recipient, in incremental allotments, of their ever-growing holdings. The Thaws had established their own foundation, the Eugene V. and Clare E. Thaw Charitable Trust, in 1981, using the proceeds from the sale of a single van Gogh painting. The trust supports the arts, the environment and, of particular importance to Ms. Thaw, animal rights. In 1987, the Thaws moved from their farm in Cherry Valley, in Otsego County, to Santa Fe, N.M. There they began collecting Native American art, eventually acquiring more than 1,000 objects. They later gave the entire collection to the Fenimore Art Museum in Cooperstown, N.Y., not far from Cherry Valley. A wing designed by Hugh Hardy was built in 1995 to house it. The Thaws returned to Cherry Valley five years ago, and Ms. Thaw died there in June at 93.Mr. Thaw is survived by a son, Nicholas, and a granddaughter.