7. Oswin
In the Series 7 premier Asylum of the Daleks, The Doctor and his companions are lured into the Parliament of the Daleks. They inform him of the asylum they send their post-traumatic stressed compatriots to, as even the Daleks fear these mad machines. Instead of trying to exterminate the doctor, they have now acquired him for assistance in de-activating the force field protecting the planet so that they can destroy it before the insane Daleks escape. While on his journey, the Doctor intercepts a message consisting of portions of the opera Carmen. He ultimately discovers that the message is from a foxy young lady named Oswin Oswald, a sharp-tongued crash survivor who has been stranded on the planet for a year, successfully avoiding being morphed into a Dalek like other visitors of the planet and biding her time by cooking souffles. Oswin, played by the current companion Jenna-Louise Coleman, is charming and demonstrates a quick-witted back and forth rapport with the Doctor instantly. A brilliant mind, Oswin is also the key to unlocking the force field which will successfully conclude the Doctor's mission. When the Doctor, with the aid of Oswin, manages to evade the onslaught of Daleks and reach Oswin's chamber, he's devastated to find that she is not who she believes she is. The Oswin she once was had since been transformed into a Dalek; it was only through her sheer will to live that she maintained her last shreds of humanity. The end is bittersweet, as Oswin's demise is a tragic one. But as the audience, we know that the success of this character is a good omen for future episodes with Number 11 and his new companion. And good god, those dimples.