10 Doctor Who Episodes More Important Than You Realised
9. The Rescue
Vicki is technically the third Doctor Who companion, but there's a case to be made that she's the one who defines the role in The Rescue.
Susan was the Doctor's granddaughter, so she doesn't really count, while Ian and Barbara were kidnapped! They became a close family unit over the course of their travels, but there were a few teething problems.
No such problems with Vicki, who is the first person to actually be invited to travel in the TARDIS by the Doctor.
Missing his granddaughter (who departed in the previous serial), the Doctor meets and rescues the young orphan who will become his next companion. The Rescue establishes Doctor Who's core idea of the title character as a lonely god seeking someone to share the universe with.
It's far more subtle here, but all the elements are in place over 40 years before Russell T Davies would make it the show's core ethos.
This means that The Rescue – a diverting enough two-parter involving a murder mystery on a crashed spaceship – is much more important to the history of Doctor Who than it initially seems.