Ducky is played by David McCallum, the legendary Scottish-born TV star who found unprecedented levels of fame in the 1960s playing enigmatic Russian agent Illya Kuryakin in "The Man From U.N.C.L.E."

The series paired him with Robert Vaughn as two James Bond-style secret agents (indeed, James Bond creator Ian Fleming reportedly helped come up with the series premise, but was not credited); Robert Vaughn played American agent Napoleon Solo and McCallum played the Russian Kuryakin. They worked for the United Network Command for Law Enforcement (U.N.C.L.E.) to fight enemies of peace around the world, most often agents of T.H.R.U.S.H. (the acronym was never explained in the series, but in a series of novels that followed it was broken down as Technological Hierarchy for the Removal of Undesirables and the Subjugation of Humanity).

The series was a huge hit. Though it's hard to believe considering the eccentric and awkward character he plays on "NCIS," McCallum was a huge sex symbol in the '60s, with a Beatles-style haircut and fan clubs full of screaming girls.

However prior to starring in "U.N.C.L.E.," which ran from 1964 to 1968, McCallum was already known to some for his (albeit smaller) role in the big-screen classic "The Great Escape."

He played Lt.-Cmdr. Eric Ashley-Pitt in that film, on the set of which he met American screen great Charles Bronson. It was in retrospect a sad sort of friendship, as McCallum's wife Jill Ireland would leave him a few years later to be with Bronson, McCallum having introduced them.

For whatever reason, McCallum never really took to screen acting the way he did television. He starred in many series over the years, and though none ever brought him the fame that "U.N.C.L.E." did.

He played the title character in NBC's "The Invisible Man" from 1975 to '76, then headed back home to Britain to play in the hit sci-fi series "Sapphire & Steel."

Some who won't recognize his face may still recognize his voice - he's been busy lately as a voice actor, in his spare time between "NCIS" shoots. He voices the talking car, aptly named C.A.R., in the Disney Channel cartoon "The Replacements." Interestingly enough, that character is an homage to the '80s "Knight Rider" series and its talking car KITT, and in the late '90s McCallum guest starred on the "Knight Rider" spinoff series titled "Team Knight Rider" (though not as the car).

He of course now stars as Dr. Donald (Ducky) Mallard on the CBS crime-procedural series "NCIS," the biggest series -- and role -- he's had since "U.N.C.L.E."