David McCallum, whose acting career spanned more than five decades, died of natural causes on Monday at New York Presbyterian Hospital at the age of 90, his wife of 56 years, Katherine, said.

“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,” CBS said in a statement.

McCallum was born in Scotland and had several parts in movies ("A Night to Remember," "The Great Escape," and "The Greatest Story Ever Told" as Judas) before he was cast in "The Man From U.N.C.L.E." in 1964 and became a star.

The other major show McCallum starred in was "NCIS", which started in 2003, almost 40 years after his previous one.

His final role

McCallum starred as the popular medical examiner "Ducky" Mallard on the show, which dealt with crimes involving the Navy and Marines and starred Mark Harmon as Gibbs.

McCallum said he thought his character looked "silly" in a bow tie but was fun to do.

He played Ducky until the last few seasons of the show, when he appeared sporadically rather than as a regular character. By then he was well into his 80s.

“He was a scholar and a gentleman, always gracious, a consummate professional, and never one to pass up a joke. From day one, it was an honor to work with him and he never let us down. He was, quite simply, a legend," a statement from ”NCIS” Executive Producers Steven D. Binder and David North said.

In between

Between "U.N.C.L.E." and "NCIS," McCallum did several other shorter shows, guest starred on a number of series, and did Broadway and off-Broadway shows.

He had two Emmy nominations for "U.N.C.L.E." and another one for a 1969 Hallmark Hall of Fame drama called “Teacher, Teacher" in which he portrayed an educator with an alcohol addiction.

He became an American citizen by the 1960s, and said in 2003, “I have always loved the freedom of this country and everything it stands for. And I live here, and I like to vote here.”

“He was a true Renaissance man — he was fascinated by science and culture and would turn those passions into knowledge. For example, he was capable of conducting a symphony orchestra and (if needed) could actually perform an autopsy, based on his decades-long studies for his role on NCIS,” son Peter McCallum said in a statement.

"The kindest man"

Speaking about his career, McCallum told a reporter in 2007, “I’ve always felt the harder I work, the luckier I get. I believe in serendipitous things happening, but at the same time, dedicating yourself to what you do is the best way to get along in this life.”

NCIS costar Lauren Holly said of McCallum on X: “You were the kindest man. Thank you for being you.”

The 20th anniversary “NCIS” marathon on Monday night on CBS included an “in memoriam” card in remembrance of McCallum.