George Peppard originally was offered the role of "Blake Carrington" but Peppard's refusal to play Blake with the shades of moral ambiguity that the writers wrote for Blake caused them to go with their second choice, John Forsythe.
Shay Duffin was the original actor chosen for playing Joseph. He even shot the first pilot along with George Peppard in April 1980. When the pilot was re-shot in October 1980, Duffin was replaced by Lee Bergere.