Duncan was nominated for an Oscar for his portrayal of a death row inmate in "The Green Mile." He worked for Peoples Gas in Chicago before getting his first role in "Armageddon" in 1998.
His publicist says Duncan never fully recovered from a heart attack he suffered July 13.
"Michael was a close friend," said White Sox GM Kenny Williams. "He was the nicest, kindest guy anyone could ever know. He was a great fan of the Chicago White Sox and often called me to offer advice. His friendship will be missed."
Duncan was one big, irresistible jumble of contradictions.
His presence was formidable, even intimidating: The former bodyguard had a muscular, 6-foot-4 frame, but it was topped by the brightest of megawatt smiles.
His gravelly baritone was well-suited to everything from animated films to action spectacles, but no matter the role, a warmth and a sweetness was always evident underneath.
The prolific character actor, whose dozens of movies included ''Planet of the Apes" and "Kung Fu Panda," died Monday at age 54. And although he only turned to acting in his 30s, it's clear from the outpouring of prayers and remembrances he received across the Hollywood and sports worlds that his gentle-giant persona made him much-loved during that relatively brief time.
Duncan died at Cedars-Sinai Medical Center in Los Angeles, where he was being treated for a heart attack, said his fiancée, reality TV personality Rev. Omarosa Manigault, in a statement released by publicist Joy Fehily.
Duncan "suffered a myocardial infarction on July 13 and never fully recovered," the statement said. "Manigault is grateful for all of your prayers and asks for privacy at this time. Celebrations of his life, both private and public, will be announced at a later date."
Tom Hanks, star of 1999's "The Green Mile" - the film that earned a then-little-known Duncan a supporting-actor nomination at the Academy Awards - said he was "terribly saddened at the loss of Big Mike. He was the treasure we all discovered on the set of 'The Green Mile.' He was magic. He was a big love of man and his passing leaves us stunned."
"I will miss my friend, Michael Clarke Duncan," comedian and talk-show host Steve Harvey said on Twitter. "What an incredible soldier in God's Plan." Other sad and shocked reactions came from a diverse field that included Dallas Mavericks owner Mark Cuban, actresses Alexa Vega, Niecy Nash and Olivia Munn, and former boxing champion Lennox Lewis.
In the spring of 2012, Duncan had appeared in a video for PETA, the animal rights organization, in which he spoke of how much better he felt since becoming a vegetarian three years earlier.
"I cleared out my refrigerator, about $5,000 worth of meat," he said. "I'm a lot healthier than I was when I was eating meat."
Duncan had a handful of minor roles before "The Green Mile" brought him accolades and fame. The 1999 film, based on the Stephen King novel of the same name, starred Hanks as a corrections officer at a penitentiary in the 1930s. Duncan played John Coffey, a convicted murderer with a surprisingly gentle demeanor and extraordinary healing powers.
Duncan's performance caught on with critics and moviegoers and he quickly became a favorite in Hollywood, appearing in several films a year. He owed some of his good fortune to Bruce Willis, who recommended Duncan for "The Green Mile" after the two appeared together in "Armageddon." Duncan would work with Willis again in "Breakfast of Champions," ''The Whole Nine Yards" and "Sin City."
His industrial-sized build was suited for everything from superhero films ("Daredevil") to comedy ("Talladega Nights," ''School for Scoundrels"). He could have made a career out of his voice work alone, with appearances in several animated and family movies, including, "Kung Fu Panda," ''Racing Stripes" and "Brother Bear." Among Duncan's television credits were "The Apprentice," ''Two and a Half Men," ''The Suite Life of Zack and Cody" and a new series, "The Finder."
Born in Chicago in 1957, Duncan was raised by a single mother whose resistance to his playing football led to his deciding he wanted to become an actor. But when his mother became ill, he dropped out of college, Alcorn State University, and worked as a ditch digger and bouncer to support her. By his mid-20s, he was in Los Angeles, where he looked for acting parts and became a bodyguard for Will Smith, Jamie Foxx and other stars. The murder of rapper Notorious B.I.G., for whom Duncan had been hired to protect before switching assignments, led him to quit his job and pursue acting full-time.
Early film and television credits, when he was usually cast as a bodyguard or bouncer, included "Bulworth," ''A Night at the Roxbury" and "The Players Club."