I would disagree, Gates was great in the role of Doctor Crusher, but I must say Diana Muldaur was far worst Star Trek actor. Why in the world, they gave her a chance to replaced Gates McFadden during one season of TNG. Thank God, that they made agreement to bring back Gates after just one season with Diana Muldaur. Also, Diana appeared in one episode of TOS and she wasn't very good in that episode too, and that is when she was much younger.
...and I disagree with you, Keith1701. While I am fine with Gates McFadden, Diana Muldaur was possibly the best doctor in all of 24th century Trek. Her character made an excellent foil for Picard; finally, someone to stand up to him! There was never any intent for her to stay more than one season. She was there while Gates McFadden had her baby.
My vote for worst Star Trek actor ever would be Marina Sirtis. She may have had black hair, but she acted like a "stereotypical dumb blonde" throughout most of TNG.
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