Michael Jackson’s damaged reputation began to recover the day he died.

The lurid accusations of child molestation that had dogged him for years fell to the background as fans around the world celebrated the entertainer who had gone from pop prodigy to global superstar over a four-decade career. Flash mobs from Stockholm to the Philippines re-enacted his video scenes, and his music sales again broke chart records.

Now, nearly 10 years after his death, the dark side of Mr. Jackson’s legend has returned through a documentary that rocked the Sundance Film Festival and is being championed by Oprah Winfrey. In addition to delivering a hit to his mended reputation, the film poses a significant risk to the Jackson estate, which has engineered a thriving posthumous career, including a Broadway-bound jukebox musical.

The four-hour documentary, “Leaving Neverland,” to be broadcast on HBO in two parts on Sunday and Monday, focuses on the wrenching testimony of two men, Wade Robson and James Safechuck, who say Mr. Jackson abused them for years, starting when they were young boys. While the accusations are not new, their revival in the #MeToo era, with its momentum of accountability for figures like R. Kelly, Harvey Weinstein and Bill Cosby, gives them new meaning.

“There has always been this shadow or cloud about Michael,” said Charles Koppelman, a longtime music executive who once served as a financial adviser to Mr. Jackson. “With this documentary about to be shown to millions and millions of people, and all the notoriety that it’s now getting, I think it will have a detrimental effect to the legacy and the estate.”