10 Doctor Who Characters More Important Than You Realised

10. Bill's Housemate Harry

As featured in Series 10's Knock Knock, Bill's housemate Harry seemed like a nice enough young man who was destined to be bumped off by David Suchet's creepy landlord. It's a good job that Harry survives his ordeal in the end, because an old friend of the Doctor's would never have forgiven him.

That's because writer Mike Bartlett revealed to Doctor Who Magazine that it was his intention to make Harry the grandson of Fourth Doctor companion Harry Sullivan! The line was ultimately cut from the finished script, making it hard to figure out if this was the same grandfather who tried to steal a bit of the Great Wall of China with his boyfriend.

Regardless, it adds a completely new dimension to the story, as the Doctor and young Harry teaming up now has more emotional resonance in retrospect.

He gets quite a horrific "death", being devoured by the Dryads after putting his foot through a rickety step. Imagine the Twelfth Doctor having to pay a visit to his old pal Harry Sullivan to inform him about his grandson.

Thankfully, the Doctor and Bill convince Eliza to end the charade that she and her son have been maintaining, reconstituting all of Bill's friends and saving the Doctor from a very awkward conversation.