The producers for Rocky III were looking to cast the villain for the movie, Clubber Lang.  They were looking for someone "tough, mean, disgusting, ugly, and believable".  Joe Frazier and Jim Brown were considered, as was boxer Matthew Saad  Muhammed.  Muhammed turned it down by saying "I can be mean, tough, disgusting and believable as a heavyweight champion. But ugly?  Can't look ugly."  They got Mr. T for the part.