Budd Hopkins, a distinguished Abstract Expressionist artist who — after what he described as a chance sighting of something flat, silver, airborne and unfathomable — became the father of the alien-abduction movement, died on Aug. 21 at his home in Manhattan. He was 80.

The cause was complications of cancer, his daughter, Grace Hopkins-Lisle, said.

A painter and sculptor, Mr. Hopkins was part of the circle of New York artists that in the 1950s and ’60s included Mark Rothko, Robert Motherwell and Franz Kline.

His work — which by the late ’60s included Mondrian-like paintings of huge geometric forms anointed with flat planes of color — is in the collections of the Metropolitan Museum of Art and the Museum of Modern Art in New York, the Corcoran Gallery of Art in Washington and the British Museum, among others.

In later years Mr. Hopkins turned to large, quasi-architectural sculptures that seemed to spring from primordial myths. In 1985, reviewing one such piece, “Temple of Apollo With Guardian XXXXV” — it was part house of worship, part archaeological ruin, part sacrificial altar — Michael Brenson wrote in The New York Times:

Budd Hopkins in Roswell, N.M., in 1997. Credit Chang W. Lee/The New York Times

“If the work is about sacrifice and violence, it is also about ecstasy and illumination. In the course of trying to re-establish the broadest meaning of the abstract geometry that has fascinated so many 20th-century artists, Hopkins makes us consider that ritual, worship, cruelty and superstition have always been inseparable.”

Some articles about Mr. Hopkins made much of the relationship between these pieces and his fascination with otherworldly visitors, for by then his books, lectures and television appearances had made him well known as a U.F.O. investigator. Mr. Hopkins, however, disavowed a connection.

He was also quick to point out that he had never been abducted himself. But after what he described as his own U.F.O. sighting, on Cape Cod in 1964, he began gathering the stories of people who said they had not only seen spaceships but had also been spirited away in them on involuntary and unpleasant journeys.

As the first person to collect and publish such stories in quantity, Mr. Hopkins is widely credited with having begun the alien-abduction movement, a subgenre of U.F.O. studies. Later high-profile writers on the subject, including Whitley Strieber and the Harvard psychiatrist John Mack, credited him with having ignited their interest in the field.

In eliciting the narratives — many obtained under hypnosis — of people who said they had been abducted, Mr. Hopkins was struck by the recurrence of certain motifs: the lonely road, the dark of night, the burst of light, the sudden passage through the air and into a waiting craft, and above all the sense of time that could not be accounted for.

He went in search of that lost time. What he found, in story after story, was this:

The aliens were technically sophisticated and many spoke improbably good English. They were short, bug-eyed, thin-lipped and gray-skinned, stripped their subjects naked and probed them with instruments, often removing sperm or eggs.

These narratives, Mr. Hopkins wrote, led him to a distasteful but inescapable conclusion: The aliens — or “visitors,” as he preferred to call them — were practicing a form of extraterrestrial eugenics, aiming to shore up their declining race by crossbreeding with Homo sapiens.

In 1989 Mr. Hopkins founded the Intruders Foundation, based in Manhattan, to help sound the alarm.

 "Guardian LXVII" by Budd Hopkins, 1989. Credit Grace Hopkins-Lisle

He wrote four books on the subject, including “Intruders: The Incredible Visitations at Copley Woods” (1987), which spent four weeks on the New York Times best-seller list and was the basis of a 1992 TV movie starring Richard Crenna.

Mr. Hopkins’s work drew inevitable fire; in interviews he sometimes likened his attackers to Holocaust deniers, an analogy that incurred further criticism.

Elliott Budd Hopkins was born in Wheeling, W. Va., on June 15, 1931, and at 2 survived polio. He earned a bachelor’s degree in art history from Oberlin College in 1953 and afterward settled in New York, where he soon made his artistic reputation.

After the Cape Cod sighting he described — a silvery disc over Truro, Mass. — Mr. Hopkins began researching U.F.O.’s. In 1976 he published an article about abductions in The Village Voice, which led to an article in Cosmopolitan.

The exposure drew sacks of letters from readers wondering if they too had been abducted, and his second career was born. By the 1980s, it had eclipsed the first.

Mr. Hopkins’s three marriages, to Joan Baer, April Kingsley and Carol Rainey, ended in divorce. Besides his daughter, Grace, from his marriage to Ms. Kingsley, he is survived by his companion, Leslie Kean; a sister, Eleanor Whiteley; and a grandchild.

His memoir, “Art, Life and UFOs,” was published in 2009 by Anomalist Books.

Unlike some writers in the genre who described their own abductions as spiritually transformative, Mr. Hopkins believed that no good could come of being the unwilling subject of a vast human genome project in the sky. He called his informants “victims” and ran group therapy sessions for them in New York.

Many who shared their stories with Mr. Hopkins had no conscious memory of their abductions at first. But they had lived for years, he said, with the nagging feeling that somewhere, something in their lives had gone horribly wrong.

Their condition, Mr. Hopkins said, was not as rare as one might suppose. By his reckoning, 1 in 50 Americans has been abducted by an alien and simply does not know it.