10 Major Doctor Who Events That Changed Everything

5. 'The Ruth Doctor'

Secret incarnations of The Doctor are a bit like a interdimensionally-transcendental bus. You don't even know they exist one minute and then suddenly BAM! You've got two in one go. Not long after the success of John Hurt's War Doctor, Chris Chibnall decided to fill what fans believed would be a relatively cheery episode, featuring the Judoon in modern-day Gloucester, into a tirade of surprise reveals.

Whilst the return of fan-favourite Captain Jack was the most welcome of companion comebacks, it was the left-field reveal of optimist Ruth being an impossible incarnation of The Doctor that really sold Fugitive of the Judoon as a WTF moment amongst Whovians. Whilst the War Doctor changed the timeline of The Doctor by introducing a new incarnation as a bridging point between the Classic Series and the New Series, The Ruth Incarnation is truly an enigma as she can't be explained within the Doctor's pre-established timeline since the 1960s.

For one, this incarnation is already calling themselves 'The Doctor' which means we should rule her out as being a Pre-Hartnell Doctor, as The First Doctor is believed to be the first to adopt this name. On top of that, her TARDIS is already disguised as a British Police Telephone Box, which first happened in the original episode, An Unearthly Child. This moment within Series 12 led Jodie Whittaker's Thirteenth Doctor to question the very foundations of what is true about their history, and oh boy, does it only get more confusing from there.

However, even though The Ruth Doctor is still to be explained within the series, the pure charm and charisma of Jo Martin's performance has already cemented this mystery incarnation into the mythos of the show just as warmly as any other incarnation. A true testament to how firmly change can be embraced within the show.