Mr. Prosky - who was nominated for two Tony awards for his work on Broadway and appeared in popular movies like "The Natural" (1984), "Mrs. Doubtfire" (1993) and "Broadcast News" (1987) - epitomized the versatility of a consummate character actor; within one year he played the heads of the CIA and the KGB.

Mr. Prosky's immediate success in 1984 on "Hill Street Blues" as the replacement for the beloved desk sergeant played by Michael Conrad, who had died, reflected his acting acumen. Prosky created a wholly new character, one who combined aggressiveness, defensiveness and a penchant for ridiculous accidents. This scrupulously honed persona became synonymous with the new sergeant's signature line: "Let's do it to them before they do it to us."

Mr. Prosky, who appeared in 220 plays, 38 movies and hundreds of television shows, developed his craft at the Arena Stage in Washington, a regional theater admired for range and ambition. His two exquisite portrayals of Willy Loman in "Death of a Salesman" there are still discussed. In 1980, Mel Gussow wrote in the New York Times that Mr. Prosky represented "a certification of the effectiveness of the American regional theater movement."

In 1982, he turned down the role of Coach in "Cheers" because he could not stand the thought of playing the same role for the seven years specified in the contract.

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