Simplify the following text for a Grade 5 native English-speaking person.
Original: Thomas Mark Harmon ( born September 2 , 1951 ) is an American actor who has been starring in U.S. television programs and films since the mid-1970s , after a career as a collegiate football player with the UCLA Bruins .
Simplified: Mark Harmon ( born September 2 , 1951 ) is an American actor .