Spartacus on Spartacus

Yeah, you read that right, the title character was replaced! The reasoning is pretty tragic, though, as the original Spartacus, Andy Whitfield, had to leave the show when he was diagnosed with cancer between the first and second seasons of the show. They originally made a prequel miniseries to bide their time while Whitfield entered treatment in the hopes that he would recover and they would resume filming. Unfortunately, Whitfield passed away in 2011 and was never able to return to the show. After his passing, the role was recast with Liam McIntyre who played the role for two more seasons before the show ended.