The Scottish-born actor was best known as Ilya Kuryakin in 1960s spy series The Man from U.N.C.L.E. before he joined the cast of the US navy crime drama.
Thirteen seasons in and Mallard is one of TV’s most beloved characters. NCIS is mighty strong with more than 20 million viewers per episode in America.
“You work all day but it is such a pleasure,” McCallum says. “NCIS is like a well-oiled machine. It runs so smoothly.
“Ducky is three-dimensional rather than one dimensional and that has made a tremendous difference to me.
“At first, I knew nothing about pathology and so I worked with a coroner. He let me go in and be by the pathologist when they are performing autopsies. I got to learn all about the human body.
“My wife Katherine (Carpenter) is on the national board of the Marine Corp Scholarship Foundation so we have a strong association with (that too). I also had to know about military jurisprudence so it is a constant learning process.”
But NCIS isn’t enough. McCallum has written a crime novel, Once a Crooked Man, which was published in January.
“Many years ago I was listening to a Jack Higgins (The Eagle Has Landed) audiotape and I thought ‘I could try my hand at this’,” McCallum says.
Recent episodes of NCIS feel like they have been ripped from the headlines. Season 13 started with NCIS leader Leroy Gibbs (Mark Harmon) in surgery after being shot by a child recruit of terrorist group, The Calling.
“It is very topical with all the children recruited by ISIS and doing the most horrendous things on the internet,” McCallum says.
“The writers seem to be ahead of the headlines. We do the show and then things pop up in the news. It can be uncanny at times.”
McCallum goes into a reflective mood when asked about the recent movie remake of The Man from U.N.C.L.E.
“It was such a big change in my life leaving Britain and going to America, getting the series, and it being successful,” McCallum says.
“It also marked a big personal change because my wife Jill (Ireland) went off with Charles Bronson and I met Katherine. I met her 50 years ago and we’ve been married for 48 of them and have our children and grandchildren.”
At the start of each NCIS season, McCallum opens up his Santa Monica home, makes sure the car is working, and the next day drives to the studio.
“My cardiologist said ‘you may look 65 but you’ve got a lot of miles on you’,” McCallum says. “I do pilates twice a week. I try to move as much as I can.
“When you have to be at the NCIS set at seven o’clock in the morning, remember the lines and give a performance, I think that’s tremendously good for your health.
“It keeps you alive. I don’t want to give that up.”