Steven Moffat's 10 Greatest Additions To Doctor Who

10. Missy

After glimpses of the mysterious Missy were scattered throughout Series 8, Moffat dropped the bombshell reveal that Missy was a new incarnation of The Master, The Doctor's life-long Best Frenemy, during 'Dark Water.'

While as insane as ever, Missy is much more layered than other recent versions of The Master, her insanity manifesting itself in a rather different fashion. Where earlier incarnations of The Master were desperate to best The Doctor, Missy was instead obsessed with becoming his friend again. Most of her evil plots are formulated with this goal in mind.

The result is a much more morally complex version of the character than we were used to. A Master that genuinely grows as a character, ultimately deciding to side with The Doctor against her own past self.

The fact that Missy dies without The Doctor ever knowing that she'd chosen to stand with him is one of the greatest tragedies in NuWho.