5. Clara Oswald, "The Rings of Akhaten"
The newest companion and one already growing close to fans' hearts, the identity of the mysterious Clara Oswald - mysterious because she's already lived and died alongside the Doctor in two vastly different time periods and in different circumstances. The 21st century Clara's first adventure in the TARDIS is to an alien market where she helps save an entire an entire solar system orbiting a villainous star that eats the memories and souls of its inhabitants. It's here that Clara shines in a deeply moving moment that follows the Doctor's tearful revelations. Clara offers up her most valuable possession - the leaf that led to her parents meeting and her birth and one that meant her mother gave up her dreams of travelling, an entire infinity of untapped potential and possibilities - and it vanquishes the 'old God', saving everyone and proving Clara's current mettle as someone trying to grow up and move on , saving the world through as painful a catharsis as we could imagine as she does so.