Few subjects, if any, were off limits for Mr. Donahue, who was said to have told his staff, “I want all the topics hot.” It mattered little that at times the subjects made some viewers, and local station managers, squirm. His very first guest was guaranteed to stir controversy: Madalyn Murray O’Hair, at the time America’s most famous, and widely unpopular, atheist.

Across the years — he moved from Dayton to Chicago in 1974, and then to New York in 1985 — he interviewed presidential candidates and Hollywood stars, consumer advocates and feminist pioneers. He also televised a child’s birth, an abortion, a reverse vasectomy and a tubal ligation. From inside a maximum-security prison in Ohio, he examined the American penal system. He was among the first television hosts to explore the AIDS epidemic of the 1980s, and the first Western journalist to go to Chernobyl, in Ukraine, after the 1986 nuclear accident there.

And there was sex, lots of it — more and more as the years passed. Not every conversation qualified as lofty discourse, not with Mr. Donahue donning a dress and stockings to study cross-dressing, or interviewing lesbian go-go dancers, or exploring the merits of dressing up like a baby for sexual pleasure.

He offered no apologies for his frequent traipses down the low road. “This is a medium that rewards popularity, and I don’t want to be a dead hero,” he told The New York Times in 1984. “Besides, it doesn’t do any good to talk if nobody’s listening.”

People indeed listened for a long time, through nearly 7,000 shows that won a total of 20 Daytime Emmy Awards. At its peak in the late 1970s and early ’80s, “Donahue” — the title shortened to a single word — was syndicated to more than 200 stations around the country, with an average viewership of eight million. People waited 18 months for studio tickets. For a while, Mr. Donahue also had a regular interview segment on NBC’s “Today” show.