Fan

Fans were people who had a strong interest in something or somebody. Before realising that he was his future incarnation, the Fifth Doctor initially believed that the Tenth Doctor was a fan, suspecting that he was a member of LINDA. (TV: Time Crash) The Whizz Kid was a fan of both the Psychic Circus and Captain Cook. (TV: ''The Greatest Show in the Galaxy)

The Ninth Doctor identified himself as a fan of Charles Dickens. With Dickens unfamiliar with the term, the Doctor clarified that the term was short for "fanatic". (TV: The Unquiet Dead)

Invalid sources
A fan of the Doctor attended the Annual Gallifreyan Doctor Who Con where they asked the first six incarnations of the Doctor and Dr. Who about the most evil foe they had encountered over the years. (NOTVALID: Doctor Who? 95)

The Cyber Fan, a variant of Cyberman, asked the Seventh Doctor for his autograph. (NOTVALID: Doctor Who? 204)