Don Buchwald, Howard Stern's Longtime 'Super Agent,' Dead at 88

Don Buchwald -- the iconic super-agent who started his own firm and who's repped tons of stars, including Howard Stern -- has died ... TMZ has learned.

The longtime Hollywood power player's agency confirmed the sad news -- explaining he passed Monday at his Massachusetts home surrounded by loved ones. We're told he died of natural causes.

Don formed his bi-coastal agency Buchwald with five associates in 1977 -- and over the years, he built it into a leader for Hollywood representation ... in the areas of commercial, broadcast, film, theater, television, literary and emerging talent.

Among the current list of agency clients ... Jason Priestley, Jean Smart, Robert Patrick, Keith David, Jason Lee, Holt McCallany, Natasha Henstridge, Dominic Monaghan and Michael Rosenbaum.

Of course, his biggest client was Stern. DB repped Howard personally, while also acting as his manager and publicist. HS was Don's single personally handled client ... and Howard referred to "superagent Don Buchwald" over the years on the radio.

And for Howard ... Don was super ... as he helped to land the radio personality with an eye-popping contract worth an estimated $90 million a year at SiriusXM!!

Don may have been surrounded by celebs every day ... but he had no interest in being in the spotlight ... telling the New York Times in 2018, “I’m not a particularly boastful person." Meaning, it was all about the business and not so much about the show.

He was 88.