Other than Burt Young (Paulie), none of the primary actors in Rocky were the first choice. Producers wanted Lee Strasberg for Mickey, but he wanted too much money. Burgess Meredith, a professional actor since the 1930s, stepped in. Boxer Ken Norton was lined up to play Apollo, but he dropped out at the last minute to go on the ABC show Superstars. Carl Weathers auditioned shortly after and got the part, even though he insulted Stallone’s acting during his read through and lied about having boxing experience! 
