The Jeffersons
This is a crazy story. The character of Lionel Jefferson was known for Damon Evans' portrayal, but he was first played by Mike Evans. Evans' only issue was that he wasn't part of the family! Don't worry though, because Mike returned toward the end of the series for a few seasons, so the family was reunited once again!
Private Practice
Naomi wasn't always played by Audra McDonald. In fact, she was first played by an actress named Merrin Dungey This swap was due to “a chemistry thing between Merrin and Taye Diggs, who played Naomi’s estranged husband, Sam." Shonda Rhimes was especially hurt by the recast, as she and Merrin were very close friends.