Mark Harmon, best known for his iconic portrayal of Leroy Jethro Gibbs on NCIS, had a rather unusual start in show business, thanks to his famous father, Tom Harmon. A celebrated football player for the Michigan Wolverines and the Los Angeles Rams, Tom later became a spokesperson for Kellogg’s now-discontinued cereal, Product 19.
As part of his father’s endorsement deal, Mark was enlisted to appear in a backyard cereal commercial, an experience he later described as “humiliating.” During an appearance on Live with Kelly and Mark, the actor recounted the moment, saying, “My dad was a spokesperson for Product 19, and I was in a commercial, in the backyard eating cereal … which, that never happened.” Mark admitted the experience was embarrassing and revealed he didn’t even get paid for it. Despite the awkwardness, the experience left a lasting impression. It introduced him to the entertainment world and sparked a deeper interest in acting. “It changed my direction a little bit,” he shared, reflecting on his early exposure to the industry.
Mark’s first official acting role came in 1973 with a one-episode appearance on Ozzie’s Girls, according to IMDb. From there, he built a steady resume of minor roles before landing his first recurring gig as Officer Mike Breen on Sam, a role that foreshadowed his future as an onscreen investigator. Over the years, Harmon became a familiar face on television with prominent roles on shows like St. Elsewhere and Flamingo Road. In 1991, he took on another law enforcement role in Reasonable Doubts.
Before joining NCIS, Mark spent several years portraying Dr. Jack McNeil on Chicago Hope, wrapping up that role in 2000. In 2003, he made his debut as Gibbs, a role he played for 435 episodes before stepping away to pursue other projects. His departure led to Gary Cole taking over the investigative mantle on the series.
Mark hasn’t completely left the NCIS universe, however. He returned as a narrator for NCIS: Origins, a spin-off exploring the early career of his beloved character. Harmon has been heavily involved in the creation of the spin-off, offering fans a chance to see more of Gibbs’ story while continuing his legacy within the franchise.
