Previous Doctor Who companion Ian Chesterton had been a history teacher. Nyssa, another companion, was a genius scientist, while a third, Jamie McCrimmon, was a Highland Scot from the mid-18th century. Davies wanted his Doctor’s companions to be ordinary — and to that end, his first, Rose, was a teenage girl who lived at home and worked in a shop. She was designed to be someone aspirational, allowing viewers to see themselves.
Though companions had always been a stand-in for the audience, a conduit into the world of Doctor Who, the companions Davies dreamed up were the personification of the ordinary young adults the show wanted to attract. Rose Tyler, Mickey, Donna, and the companions that would follow were more than audience surrogates — they were the audience, in a very direct way.
Beyond Davies’ tenure, we can see how this influenced the series that followed, with the likes of Amy Pond, Rory Williams, Clara Oswald, and Bill Potts. They all had different qualities that you’d find in ordinary “Doctor Who” viewers, allowing audiences to see themselves as companions of the Doctor.