His career received a significant boost in 1960 when he was cast as the smooth-talking gunfighter Harry Luck in The Magnificent Seven. Dexter's aptly-named character provides comic relief in the movie, particularly in the scenes where he quizzes various Mexican villagers regarding the whereabouts of what he believes to be is a hidden cache of riches.
He was married three times: Peggy Lee (January 1953 until they divorced in September of the same year), Mary Bogdanovich (January 1970 until her death on June 12, 1994) and June Deyer (1994 until his death on December 12, 2002).
He is best known for his role as Harry Luck, one of the title characters of The Magnificent Seven. However, he is the one of the seven whom no one can ever remember.
He was a close friend of Frank Sinatra. Their relationship began in 1964 when he saved him from drowning. Sinatra was swimming at the beach while on location during the filming of None But the Brave. He began to be pulled into the undertow along with his female co-star.
Dexter immediately sprang to his aid and was able to save them both. He was awarded by the Red Cross for his heroism. The two later had a falling out and Dexter complained about Sinatra's pettiness and the fact that he never thanked him or gave him credit for saving him.