LOS ANGELES — Actor David McCallum, who became a teen heartthrob in the hit series "The Man From U.N.C.L.E." in the 1960s and was the eccentric medical examiner in the popular "NCIS" 40 years later, has died. He was 90.

McCallum died Monday of natural causes surrounded by family at New York Presbyterian Hospital, CBS said in a statement.

"David was a gifted actor and author, and beloved by many around the world. He led an incredible life, and his legacy will forever live on through his family and the countless hours on film and television that will never go away," said a statement from CBS.

Scottish-born McCallum had been doing well appearing in such films "A Night to Remember" (about the Titanic), "The Great Escape" and "The Greatest Story Ever Told" (as Judas). But it was "The Man From U.N.C.L.E." that made the blond actor with the Beatlesque haircut a household name in the mid-'60s.

The success of the James Bond books and films had set off a chain reaction, with secret agents proliferating on both large and small screens. Indeed, Bond creator Ian Fleming contributed some ideas as "The Man From U.N.C.L.E." was being developed, according to Jon Heitland's "The Man From U.N.C.L.E. Book."

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The show, which debuted in 1964, starred Robert Vaughn as Napoleon Solo, an agent in a secretive, high-tech squad of crime fighters whose initials stood for United Network Command for Law and Enforcement. Despite the Cold War, the agency had an international staff, with McCallum as Illya Kuryakin, Solo's Russian sidekick.

The role was relatively small at first, McCallum recalled, adding in a 1998 interview that "I'd never heard of the word 'sidekick' before."

The show drew mixed reviews but eventually caught on, particularly with teenage girls attracted by McCallum's good looks and enigmatic, intellectual character. By 1965, Illya was a full partner to Vaughn's character and both stars were mobbed during personal appearances.

The series lasted to 1968. Vaughn and McCallum reunited in 1983 for a nostalgic TV movie, "The Return of the Man From U.N.C.L.E.," in which the agents were lured out of retirement to save the world once more.

McCallum returned to television in 2003 in another series with an agency known by its initials — CBS' "NCIS." He played Dr. Donald "Ducky" Mallard, a bookish pathologist for the Naval Criminal Investigation Service, an agency handling crimes involving the Navy or the Marines. Mark Harmon played the NCIS boss.

McCallum said he thought Ducky, who sported glasses and a bow tie and had an eye for pretty women, "looked a little silly, but it was great fun to do." He took the role seriously, too, spending time in the Los Angeles coroner's office to gain insight into how autopsies are conducted.

The series built an audience gradually, eventually reaching the roster of top 10 shows. McCallum, who lived in New York, stayed in a one-bedroom apartment in Santa Monica when "NCIS" was in production.

McCallum's work with "U.N.C.L.E." brought him two Emmy nominations, and he got a third as an educator struggling with alcoholism in a 1969 Hallmark Hall of Fame drama called "Teacher, Teacher."

Bob Thomas, a longtime Associated Press journalist who died in 2014, was the principal writer of this obituary.