4. River's Regenerations
During the events of A Good Man Goes to War, fans finally discovered the truth about River Song. Not only was she a crazy haired temptress from the Doctor's future, past (or both, depending on the occasion), she was also the child of Amy and Rory Williams. What was even more interesting about River Song is that she, for all intents and purposes, was a Time Lord, too. Having been conceived whilst travelling through the time vortex, River had been, as the Doctor so cleverly put it, "cooked up" on the night of Amy and Rory's honeymoon. Following Amy's abduction at the hands of the Silence, fans found out that baby Melody had been taken away and conditioned to become the Doctor's perfect assassin. Once conditioned, she was returned to Earth where she would wait for the perfect opportunity to kill him, subsequently regenerating into Amy's childhood friend Mels. In the eighth episode of Series 6, Let's Kill Hitler, Mels was shot and regenerated into River, who at this point didn't know she was called River, and wasted no time in killing the Doctor by kissing him with poison lipstick. At the end of this episode, and with tears in her eyes, Melody asks Amy "Who is River Song?" before being shown who she will one day become. At this moment, Melody realises just how important the Doctor would be to her past, present and future before sacrificing her remaining regenerations in order to bring him back from his untimely death. Melody Pond became River Song and in turn, one of the most important parts of the Doctor's life.