The Doctor was deliberately constructed as a character against stereotype: a “cranky old man” yet also as vulnerable as a child, an anti-hero playing against the more obvious “ physical” hero of the school teacher Ian (played by the well-known lead actor in commercial televisions Ivanhoe series). Its famous, haunting signature tune was composed at the new BBC Radiophonic Workshop, adding a futuristic dimension to a series that would never be high on production values. The program always attracted ambitious young directors, with (the later enormously successful) Verity Lambert as its first. The decision to continue with the Series in 1966 when Hartnell had to leave the part and to regenerate the Doctor on screen allowed a succession of quirkily different personas to inhabit the Doctor. When it was decided in 1966 to reveal where the Doctor came from (the Time world of Gallifrey), a different way– via the strangely varied characterization. Following Hartnell, the Doctor was played by the Chaplinesque “space hobo” Patrick Troughton; the dignified “establishment” figure of Jon Pertwee; the parodic visual mix of Bob Dylan and Oscar Wilde, Tom Baker; the vulnerable but “attractive to young women” Peter Davidson; the aggressive and sometimes violent Colin Baker; the gentle, whimsical Sylvester McCoy; and, in the 1996 movie, the romantic and emotional Paul McGann. 

These shifts in personas were matched by shifts in generic style, as each era's producers looked for new formulas to attract new audiences. the mid 1970s, for example, under producer Philip Hinchcliffe, achieved a high point and audience ratings and was marked by a dramatic gothic-horror style. This led to a “TV violence” dispute with Mary Whitehouse’s National Viewers and Listeners Association. The subsequent producer, Graham Williams, shifted the series to a more comic signature. This comedy became refined as generic parody in 1979 under script editor Douglas Adams ( author of Hitchhiker's Guide to the Galaxy). Doctor Who's 17th season, for which Adams edited scripts and wrote certain episodes (“The Pirate Planet”  and “The City of Death”), became notorious with fans, who hated what they saw as the self-parody of the Doctor Who as “Fawlty Towers in space” (John Cleese appeared briefly in a brilliantly funny parody of art critics in “The City of Death”).

Throughout Doctor Who’s changes, however, the fans have remained critically loyal to the series. Fiercely aggressive to some producers and to some of the show’s signature players, the fans’ intelligent campaigns helped keep the program on the air in some of more than 100 countries where it has screened; and in the United States, huge conventions of fans brought Doctor Who a new visibility in the 1980s. However, the official fans have never amounted to more than a fraction of the audience. Doctor Who achieved the status of an institution as well as a cult.

Doctor Who’s reputation attracted high-level, innovative writers; its formula to educate and entertain encouraged a range of storylines from space opera through parody to environmental and cultural comment. Its mix of current technology with relatively low budgets attracted ambitious young producers and led to what one producer called a “cheap but cheerful” British show that fascinated audiences of every age-group worldwide. Above all, its early, ambiguous construction opened the show to innovative, often bizarre, but always dedicated acting. With so many different characterizations and acting styles, the program, like the Doctor, was continuously “regenerated” and so stayed young.