Doctor Who has always been a show of missed opportunities and what ifs, both within episodes and the grand history of the show. What if the Doctor got mixed up with Madame du Pompadour? What if he had an opposite-sex clone? What if he accidentally got engaged to an ancient Aztec woman? Sometimes the episodes have played out wonderfully and other times theyve left the fans wanting more, or less, or something completely different. Dozens of one-shot or secondary characters that should have been companions or treated differently. Why would you hire John Simm to reprise his role as the Master after a fantastic first turn, and then waste two episodes on him running round screaming and fixating on food? Why hire the daughter of the Fifth Doctor, to be the daughter of the Tenth Doctor, just to have her fly off into the sunset and never heard of again? And then, sometimes they do get it right the first time and we simply want to see the characters again. But what other one shot or recurring characters have a plausible chance of returning to the show? We're not going to see Carey Mulligan or Kylie Minogue filming in Cardiff for a year any time soon, so what other characters should return to the show, even just for a one off episode? Here are five characters that should no, must have another shot on the series and their return is plausible too.