David McCallum hated this one thing about Mark Harmon on the ‘NCIS’ set – real reason revealed

David McCallum’s passing has been tough on everyone, not least on his family. They were able to be by his side and say their last goodbyes before he passed away, and now, the NCIS star has been honored by family, friends, and former colleagues. That includes his former co-star, Mark Harmon.

David and Mark worked together for many years on NCIS. Given that they were colleagues for so long, they usually spent many hours together, both on and off set. But during shooting, sometimes the actors and crew like to do fun things to keep the spirit up.

Mark Harmon was the main prankster on the NCIS set. However, some people were intentionally left out of these shenanigans. Years ago, David McCallum revealed the real reason why his co-star never played any practical jokes on him.

David McCallum

David McCallum was a loved actor and musician throughout his entire career. But compared to many others in the business, he found success having two completely different careers in different eras.

Born on September 19, 1933, in Glasgow, Scotland, McCallum followed in his parents’ footsteps by becoming a musician. He studied at the Royal Academy of Music in London, England, but not long after, he left for the Royal Academy of Dramatic Art.

In 1946, he joined the Actors’ Equity and began working for BBC Radio. Then, several years later, in repertory theater. It was there that McCallum starred in several productions, such as Julius Ceasar and Amadeus.

After McCallum moved to the US and was cast as Illya Kuryakin in the television hit show The Man From U.N.C.L.E, success came fast. He was nominated for two Emmy Awards for his performance.

The Man From U.N.C.L.E ended up being a huge hit, with McCallum staying on the show for a total of 105 episodes over four years.

While he may have been starstruck when he met the guest stars on The Man From U.N.C.L.E, by the time the series reached the pinnacle of its success, the Scottish actor had become a major star in his own right.

According to an interview with Press & Journal, David received more fan mail than anyone else in Metro-Goldwyn-Mayer’s history, including superstars like Elvis Presley. Once, he visited the White House, and while being escorted to meet the President, a Secret Service agent told him: “You’re the reason I got this job.”

David McCallum
Silver Screen Collection/Getty Images

In the mid-1960s, McCallum landed a record deal, releasing four albums with Capitol Records. He worked with composer and producer David Axelrod, recording his own songs and interpretations of many famous hits, including I Can’t Get No SatisfactionLouie Louie, and Downtown.

Some of McCallum’s songs became huge years later. His most famous song, The Edge, was sampled by rap artist Dr. Dre as the intro and riff for his track The Next Episode.

David McCallum as Ducky on ‘NCIS’

McCallum was a massive star and a fan favorite throughout the 1960s. In later years, he garnered a new, younger crowd thanks to his performances on NCIS. In 2003, he appeared on the hit show for the first time as Ducky and never left.

“I was working with Jim Dale on (New York’s) Park Avenue back in 2002 when I got a call from my agent asking me if I was interested in auditioning for the role of a lecherous doctor in a new medical drama,” McCallum recalled.

“I thought to myself, ‘Why not?’”

The same day, McCallum found out that he had nailed the audition. So he landed the part, and the rest is history. To date, McCallum has starred as Ducky in 423 episodes of the show. A by-product is that his fanbase has once again grown to monolithic proportions. However, that didn’t only span to fans but also co-workers.

Over the years, David McCallum had worked with many talented actors, and some of them were even considered idols in his eyes. Once he was cast on NCIS, it turned out that he was someone who other very prominent actors looked up to.

David worked with the likes of Sean Murray and Pauley Perrette through his NCIS stint. However, maybe the most prominent star was Mark Harmon, starring as the one-and-only Leroy Jethro Gibbs.

Shutterstock/Joe Seer

According to reports, when Harmon met David McCallum for the first time, he was starstruck. The two appeared on a 2003 episode of JAG together. Harmon was excited to meet McCallum, saying he couldn’t believe he was shaking the famous hand of Illya Kuryakin, McCallum’s character in The Man from U.N.C.L.E.

“I can’t imagine I’m shaking the hand of Illya Kuryakin,” executive producer Steven D. Binder recalled Harmon saying. For his part, McCallum had a hilarious reaction: “Good God, man, that was 40 years ago!’”

Rocky relationships on set

Life on the set at NCIS was good for David McCallum. However, as in any other workplace, there was sometimes friction between the actors.

For example, Mark Harmon and Pauley Perrette’s relationship deteriorated, and in the end, Pauley decided to leave the show because of it.

In 2017, following 15 seasons on the show, Perrette announced she was leaving NCIS. Just days after, she took to X (then formerly known as Twitter), where she implied she’d left the show due to “multiple physical assaults.”

According to several news outlets, Perrette and Harmon’s relationship had turned rather icy due to a dog bite on set.

In 2019, she wrote on X that she was “never going back to NCIS” and was “terrified” of lead actor Mark Harmon.

Speaking with USA Today, she declined to discuss her tweets further.

“That is a part of my past now, and it’s nothing that I have any need to talk about again, other than one thing: I’m certainly grateful for having the opportunity to play that character and I always will be,” she said.


While Mark Harmon and Pauley Perrette’s feud ended as she let the set, David McCallum continued with his work on NCIS. At the time, he had also become an author, releasing his first novel, Once a Crooked Man, in 2016.

Co-stars David McCallum & Mark Harmon had a special relationship

McCallum once called NCIS his “Rock of Gibraltar,” mainly because of his working relationship with Mark Harmon. That feeling was, to say the least, mutual.

“I’ll always remember David McCallum,” Harmon said in 2019. “And I thought that from day one here, because I thought how fortunate this entire cast, whoever it is, is lucky enough to work with him and watch his work ethic every day. And take from his experience, what he’s had in this industry, for a number of years, in different shows.”

Spending hours on set every day must have been enjoyable. In fact, many people would say actors have the best job in the world, getting to travel the globe and shoot films and television series in exotic locations. But while on a show like NCIS, much of the shooting occurs in just one studio or at least one city.

In Mark Harmon and David McCallum’s case, being on such a show for so many years could probably begin to feel one-sided, even though they obviously loved working there. One day, you might be sitting in your trailer for hours just waiting for your scene, and the next day (just like in Mark and Pauley Perrette’s case) you could easily get on each other’s nerves.

But there are definitely ways of keeping the spirit up. And Harmon had one very clever way of doing it: Practical jokes.

For example, the NCIS star once decided to hang a dead lizard he had found in co-star Cote De Pablo’s trailer. One might think it’s a bit creepy, but De Pablo said it was a sign that “someone out there loves me.”

Mark Harmon
Paul Archuleta/FilmMagic

“So, I came in one day, and this is a lizard that I guess he found outside. And it’s a dead lizard which he put a noose around its neck,” De Pablo once recalled.

Why Mark Harmon never played practical jokes on David McCallum on ‘NCIS’ set

“And then he hung a little note which is intended to be like a little ‘goodbye I can’t take it anymore’ note. And it actually says, ‘I couldn’t take it anymore.’ So, he hung this in my trailer, and when I came in, I was like, ‘Ah!’”

So what did Mark Harmon do to his beloved friend and co-star David McCallum? Well, it was pretty clear he didn’t have the nerve to play any pranks on him…

In early 2016, David McCallum set up an AMA (Ask Me Anything) thread on the popular social media platform Reddit. Fans got the opportunity to ask him whatever question they liked. Many of them were, of course, about NCIS.

For example, “Ducky” revealed the real reason why Cote de Pablo left the show but also touched on other subjects. One user apparently knew about the practical jokes and asked: “Has Mark Harmon ever played a practical joke on you? Since I have heard he is a major jokester.”

David McCallum answered: “Mark Harmon knows I am not the type to be toyed with.”

On Monday, October 9, 2022, Harmon appeared in his last episode as Leroy Jethro Gibbs. He left the show after starring in 435 episodes – 18 less than David McCallum.

David McCallum
Shutterstock/Kathy Hutchins

There have been talks about Harmon’s possible return to NCIS. However, sadly, that will be without David McCallum.

Mark Harmon’s powerful tribute to late David McCallum

On September 26, he passed away at the New York Presbyterian Hospital at age 90.

“He was the kindest, coolest, most patient and loving father, he always put family before self. He looked forward to any chance to connect with his grandchildren, and had a unique bond with each of them,” his son, Peter McCallum, shared in a statement on behalf of the family.

Peter continued: “He and his youngest grandson, Whit, 9, could often be found in the corner of a room at family parties having deep philosophical conversations.”

“He was a true renaissance man — he was fascinated by science and culture and would turn those passions into knowledge,” Peter McCallum added. “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.”

David McCallum died of natural causes, surrounded by his family. And it didn’t take long before his former co-stars honored him.

“David lived a great, full, long life,” Mark said in a statement. “I was in awe when I first met him, and all of us on the show were honored to have toed a mark opposite him. My condolences go out to [David’s wife] Katherine and his family.”

If you enjoyed this article, perhaps you’d be interested in reading why David McCallum never came to terms with his son’s death

Rest in peace, David McCallum. Please share this article on Facebook with friends and family to honor his legacy.

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