Many Doctor Who fans have theorized about the significance of the name of the latest companion, Bill Potts (played by Pearl Mackie), with a fan favorite theory being that Bill’s name is a reference to William Hartnell, the first actor to ever play the Doctor.
In a recent interview with RadioTimes, Doctor Who showrunner cleared up the issue. While Bill is not necessary named after anyone, Moffat did get the idea for the name from former companion Billie Piper (Rose), during the filming of the 50th Doctor Who Anniversary special, “The Day of the Doctor.”
“If she’s named after anyone it’s that I liked the fact that, when we were doing ‘The Day of the Doctor,’ David Tennant called Billie [Piper] Bill. I thought that was a good name for somebody so I logged it then.”
This is a very sweet origin for Bill’s name, though not one, I would say, that has any greater significance within Doctor Who canon.
If you’re wondering if this sort of casual inspiration for major Doctor Who story developments happens often, look no further than Moffat’s explanation of how the First Doctor’s return in the upcoming Doctor Who Christmas special came to be…
I wasn’t especially building towards the return of the first Doctor. Available on videotape is the exact moment where it became possible. At the New York Comic Con, last year, someone was asking me about which Doctors I wanted to be in ‘The Day of the Doctor’ And the Doctor you’d really like to meet the modern Doctor is the William Hartnell Doctor because he’s moved on so much, because that would be the entire span of the character’s life. The first Doctor would be so shocked that he is going to become this strutting megalomaniac. And so I said, ‘But we can’t do it,’ and then Peter said, ‘We could get David Bradley.’ ‘Oh yeah…!’
And thus an ingenious Doctor Who story idea was born.