O'Neal's manager, Jonathan Brandstein, says the comedian died Tuesday morning. He says in a statement many people "have lost a close and loved friend" and "all of us have lost a true comic genius."
O'Neal appeared on Conan O'Brien's and David Letterman's TV shows and was a frequent guest on the "Opie & Anthony" radio show on Sirius XM.
His performance was a highlight of last summer's Comedy Central roast of Charlie Sheen.
Sheen says in a tweet, "The entertainment world as well as the world at large lost a brilliant man." He says his tears "are for the tremendous loss" to O'Neal's "true friends and loving family."