Doctor Who: Every Doctor's DEFINITIVE Episode

15. The Aztecs (The First Doctor)

The Aztecs is an extraordinary bit of television, from its sumptuous costume design to its exploration of cultural intervention. It also just happens to contain William Hartnell's very best performance as the First Doctor.

From his moral outrage at Barbara's plan to interfere in history to his bemusement at becoming engaged, Hartnell nails every single ebb and flow of the First Doctor's arc throughout.

The relationship between the Doctor and Barbara is the beating heart of Doctor Who in its early years, and Hartnell and Jacqueline Hill are terrific here. The way that the Doctor tenderly suggests to Barbara that she's made a subtle difference by saving just one life is a touching moment that reveals to the audience that she's even changed the Doctor's mind when it comes to tampering with time.

It's not for nothing that over 40 years later, The Fires of Pompeii repeated many of the same beats with David Tennant and Catherine Tate!