10 Quintessential Doctor Who Moments From The 12th Doctor

Prior to series nine, The Doctor’s only immortal friend had been Captain Jack Harkness. Captain Jack—who also headlined the Doctor Who spinoff Torchwood—made immortality look like a blast, or at its very worst a minor annoyance easily righted by a bit of silent reflection. But that’s because Jack was a charming fellow, the type to keep his darkest feelings bottled deep inside.

Enter Ashildr—played to perfection by Game of Throne’s Maisie Williams—a young Viking girl who The Doctor accidently makes immortal during a trip to the 9th century. At first the gift seems like a blessing, but over a four-episode arc in which The Doctor comes across Ashildr in numerous different time periods, her immortality turns out to be anything but.

The years wound up wiping away the optimistic young girl from days past, replacing her with a haggard cynic, who grew to despise The Doctor and his entire mode of existence. The whole ordeal ends quite badly, with the intense hatred between her and the Time Lord ending in the death of one of his dearest companions.