10 Genius Decisions By Doctor Who Companions

Midway through Series 10, the Monks invaded Earth. Beaming their lies into the brains of everyone on the globe, they made people believe that they'd been there for years, when in fact, they'd only been there a few months.

For this, only one person was to blame: Bill Potts.

By asking the Monks to cure the Doctor's blindness, she had given them the power to take over the planet - which they did. Things got pretty bad, but eventually, Bill redeemed herself when she decided to give her own life to end the Monks' tyranny.

With the Doctor being left unconscious after a failed attempt to cancel out the Monks' propaganda broadcast, Bill steps up, fully aware that if she tries to stop them herself, she will die. But she goes through with it anyway: engaging in a psychic battle with one of the Monks, she manages to overthrow them by using the memory of her dead mother to wipe out their transmission. And as an added bonus, she also survives.

Initially though, she believed she was sacrificing herself, a brave decision in and of itself. And as it turned out, it was also a really wise decision, too, because the purity and truth of Bill's memories was exactly what was needed to erase the Monks.