For the following years, Mark Harmon has been the main character in the following television shows:
1979-1980
240-Robert, playing Deputy Dwayne "Thib" Thibideaux, 13 episodes
1981-1982
Flamingo Road, playing Fielding "Field" Carlyle, 37 episodes
1983-1986
St. Elsewhere, playing Dr. Robert Caldwell, 70 episodes
1991-1993
Reasonable Doubts, playing Detective Dicky Cobb, 45 episodes
1996-2000
Chicago Hope, playing Dr. Jack McNeil, 95 episodes
2003-present
NCIS, playing Special Agent Leroy Jethro Gibbs, every episode
And to answer the question directly, he is best known for the current show NCIS.
Mark Harmon was a contestant on the Dating Game while a quarterback at UCLA in 1972!
Flamingo Road
No. Mark Harmon was only ever on JAG when he was (as Gibbs) accusing Harm of murdering Petty Officer Singer (the NCIS spin-off).
He is an actor and he is currently acting in the television show NCIS.
Daniel Scott Harmon is not related to Mark Harmon. Daniel Scott Harmon is a writer, producer, and actor known for creating the TV show "Community" and the animated series "Rick and Morty." Mark Harmon is an actor known for his roles in "NCIS" and "St. Elsewhere." Despite sharing a last name, there is no known familial relationship between the two.
NCIS was spun off from JAG, as Mark Harmon's character appeared on JAG.
He knew only enough to get by in the show, "Reasonable Doubt(s)".
Mark Harmon learned sign language for his role as a Secret Service agent with a deaf son in the TV series "Reasonable Doubts." His character's ability to communicate with his son in sign language was an important aspect of the show's plot.
Dan Harmon is the creator of the show Community. Harmon is a producer and writer, among other things. Harmon has a weekly comedy show in Hollywood.Harmon was born in 1973.
He knew only enough to get by in the show, "Reasonable Doubt(s)".
Mark Harmon stared in NCIS as Special Agent Leroy Jethro Gibbs,Flamingo Road as Feilding Carlyle,St. Elsewhere as Dr. Robert "Bobby"Caldwell, Reasonable Doubts as Det. Dicky Cobb, and Chicago Hope as Dr. Jack McNeil.
While the television show NCIS is based on a real government organization, the character Jethro Gibbs is completely fictional. Mark Harmon is the actor who portrays Gibbs on the CBS tv series.