10 Doctor Who Mysteries You Didn't Know Were Answered
9. Who Was GUS?
Representing a shady organization that wanted to capture the Foretold, the mysterious computer GUS had been trying to ensnare the Doctor since his eleventh incarnation.
So it seemed incredibly odd that by the end of Series 8's Mummy on the Orient Express, the Twelfth Doctor never tried to learn more about GUS and what he actually was.
None of Jamie Mathieson's subsequent scripts brought back GUS either, leaving it as one of the biggest loose ends of the modern era. But that doesn't mean no answers exist!
In a blog on his website, Mathieson detailed his original plans to incorporate GUS into Series 10's Oxygen, which were abandoned when it was felt that it lacked impact as an ending.
In the original version, the sign that Bill sees read "Ganymede Systems – putting the YOU in User". That would've given us "Ganymede User Systems" – or GUS for short.
Then, at the episode's climax, the Doctor contacted Ganymede's Head Office and defeated a nefarious executive called Kline, who would've had the exact same voice as GUS.
It's a little convoluted and it's no surprise it was dropped, but it works perfectly well as head canon!