Had this actor taken the role of Derek Shepard on Grey's Anatomy, we might never have had McDreamy.

At least that's what Rob Lowe thinks. The actor, famous for countless roles over more than four decades in Hollywood, turned down the role that turned Patrick Dempsey into the medical heartthrob beloved by practically every household in America. Dempsey went on to play the role for 11 seasons before his (spoiler alert) untimely death on the show. Though, to fan's delight, he made an unexpected return in the most recent 17th season.