Like any character with a romantic connection to the Doctor, River Song was bound to be divisive. In general, she is either loved with a passion bordering on the obsessive or hated with the passion of a thousand burning suns. Because of this, River makes this list not so much as a character we wanted to kill as one we wanted to stay dead. The River Song introduced in Silence in the Library and Forest of the Dead was a strong, intelligent, witty character. The true hero of the story, she proved herself just as smart and capable as the Doctor, if not more so. And then she died. And yes, it was sad. And yes, it left a lot of unanswered questions. When she returned in The Time of Angels, she was still all the things we remembered from her first appearance. We discovered a little more about the character with each appearance over the course of Series Five and Six. But the character became weaker as the mystery around her unraveled. By the time the Wedding of River Song came around, the character had lost a lot of her edge. The fact that she would rather see the entire universe destroyed than kill the Doctor ran counter to almost everything we knew about the character so far. But, with the full extent of River's history with the Doctor now revealed and her storyline resolved, she wouldn't be returning again. And then she did. River Song reappeared in the Name of the Doctor as an ill-defined psychic/machine ghost, apparently projecting her presence from the computer systems of the Library directly into Clara's brain. River didn't really add anything to the show, other than providing a bit of fan service when the Doctor kissed her ghost. Which only he could see. Ultimately, Moffat seems unable to let a good character die, much less stay dead, instead intent on digging River up at every opportunity.