Mark Harmon turned 65-years-old on Friday (Sept. 2) and, while fans everywhere may know him for his long-standing work on CBS's "NCIS," it's worth pointing out that the popular actor has been working in television for over forty years.

After bypassing a career in professional football -- he did quite well for himself with the UCLA Bruins -- Harmon decided to pursue a career in acting. He had multiple bit parts throughout the early '70s and it was when he received his first Emmy nom for his role as Robert Dunlap in "Eleanor and Franklin: The White House Years" that really got Hollywood's attention.

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Once the '80s hit, Harmon was becoming a recognizable face on TVs everywhere. After appearing as Doug Bradbury on "The Love Boat," he returned to the series a couple years later as Rick Tucker. It was later that year, in 1983, that he won his first successful series starring role as Dr. Robert Caldwell in "St. Elsewhere."

From doctor to serial killer, Harmon's career took an interesting turn when he decided to play Ted Bundy in the made-for-TV movie "The Deliberate Stranger." A year later, he made David (Bruce Willis) and Maddie's (Cybill Shepherd) relationship a bit more complicated on "Moonlighting."

After moving to the big-screen for a spell, Harmon returned to TV with the short-lived series "Reasonable Doubts" as Detective Dicky Cobb opposite Marlee Matlin's Asst D.A. Tess Kaufman.

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From crime fighting back to practicing medicine, Harmon's performance as Dr. Jack McNeil on "Chicago Hope" really solidified that he's great at serving and protecting -- whether as a cop or doctor. That statement rings true as he soon moved back to law enforcement with the role of FBI Agent Simon Donovan on "The West Wing." And then, soon after, he landed the role of Special Agent Leroy Jethro Gibbs before.

First appearing in an episode of "JAG," titled "Ice Queen," Harmon and his "NCIS" team has thrived on television for well over a decade. And thankfully, there's no sign of him stopping anytime soon.