The actor cut an imposing screen figure and not unlike the equally husky Raymond Burr was frequently cast as ne'er-do-wells as in 1952's "Macao". Not that he couldn't play the good guy, as he more or less did in "House of Bamboo" (1955). Although he remained a busy character player for much of the 1950s, Dexter seemed on the brink of breaking through when he kicked off the 60s with a starring role as one of the titular "The Magnificent Seven" (1960). But while that film solidified or raised the profiles of his co-stars like Yul Brynner, Steve McQueen and Charles Bronson, Dexter remained a relatively unknown quantity. He shone in the supporting role of gangster Benjamin 'Bugsy' Siegel in the uninspired biopic "The George Raft Story" (1961) and a reteaming with Brynner in "Taras Bulba" (1962) but he was to become better known for his off screen associations than for his film work.
Dexter was a confidante of Marilyn Monroe and he reportedly attempted to intercede when the sex siren separated from baseball great Joe DiMaggio. He was also a pal of singer-actor Frank Sinatra but their relationship was complicated by the fact that in 1964 Dexter saved the singer from drowning. At the time, they were filming "None But the Brave" (1965) and later that same year, they appeared together in "Von Ryan's Express". Sinatra later hired Dexter to work at Artanis, the singer-actor's production company. The two parted company during the filming of "The Naked Runner" (1967). According to Dexter, the strain in their friendship began when Sinatra announced his intention to marry Mia Farrow and Dexter told him it wouldn't work. While shooting the film (which Dexter was producing), Sinatra proved temperamental and expressed his desire to leave the London location. Dexter held firm and when the star bolted, worked around his absence and completed the movie. Returning to L.A., he was informed he was fired from Sinatra's company.
Dexter continued to work as a producer (1970's "The Lawyer" which was the basis of the short-lived NBC's series "Petrocelli") and returned to acting in 1972's "Jory". Once again, though, the roles were hardly taxing, although he seemed to be having fun as a senator in "Shampoo" (1975) and as Alvin Karples in "The Secret Files of J. Edgar Hoover" (1977). By the 80s, he curtailed much of his activities, making only rare forays in the business such as producing the Karl Malden TV-movie "Skag" (NBC, 1980) and one last screen appearance in "Secret Ingredient" (1990).