NCIS star Mark Harmon’s sentimental real name and why he changed it explained as he turns 75

Mark Harmon has been a steady presence on the screen for decades, from St Elsewhere to Chicago Hope, and most famously as Leroy Jethro Gibbs on NCIS.

But did you know that Mark Harmon is not the actor’s real name?

Born on September 2, 1951, Mark’s birth certificate revealed his parents named him Thomas Mark Harmon, after his father, the legendary Heisman Trophy-winning football player and sportscaster Tom Harmon.

Tom was born Thomas Harmon, and was a football star for the Michigan Wolverines from 1938 to 1940, becoming All-American in both 1939 and 1940 and winning the Heisman Trophy, the Maxwell Award, and the AP Athlete of the Year award in 1940. He was inducted into the College Football Hall of Fame in 1954, three years after Mark was born.

Mark followed in his father’s footsteps; he accepted a football scholarship to UCLA in 1972 after completing a two-year associate degree, and helped the team rise from underdogs to contenders.

During Mark’s time with the Bruins, his beloved father – who was working as a sports anchor at this point – also handled play-by-play responsibility on broadcasts of the team, keeping the father-and-son closely connected.

© Sports Illustrated via Getty Ima

Mark went through the NFL draft process but was not picked, and chose to enter the workforce instead. However, Mark soon pivoted to acting and, because his father was so well-known, Mark decided to drop the name Thomas professionally and go by Mark. It allowed him to find his own identity in Hollywood, and he quickly caught the attention of showrunners. 

By 1977, he had garnered his first Emmys nomination for Outstanding Supporting Actor in a Miniseries or a Movie for his performance in Eleanor and Franklin: The White House Years. 

Throughout the 1980s and 1990s, he was nominated for Golden Globes and Sag Awards, and in 2002 received another Emmy nod for his powerful four-episode arc on The West Wing. 

© CBS via Getty Imag

That performance led to a two-episode backdoor stint on JAG, introducing audiences to NCIS agent Leroy Jethro Gibbs, and months later Mark was leading the CBS drama NCIS , which remains on TV to this day and is one of the longest-running shows ever.

Mark left the series in 2021 during season 19, but has returned sporadically for spinoff shows including an NCIS: Origins crossover special on Veterans Day 2025.