Is Doctor Who's main character "The Doctor" or "Doctor Who," and is there even a definitive answer to be found? Ever since Doctor Who first aired in 1963, the title character has been a man of mystery. The Time Lord (although even that wasn't mentioned until the end of the Second Doctor's reign) arrives on the screen as an enigma, no one knows where he comes from, who he is, his age or his race. All the audience know is that the Doctor champions virtues of justice and kindness while harboring a distinct thirst for adventure.
Undoubtedly the biggest question mark surrounding science fiction's iconic time-traveling nomad concerns the character's name. From his very first episode to her forthcoming New Year's Day 2020 offering, the strange leading figure consistently refers to themselves as "The Doctor." Various pseudonyms, including the ever-popular John Smith, have been deployed on occasion, but friend and foe alike have known the owner of the TARDIS by the title of "Doctor." This moniker the Time Lord chose themselves on Gallifrey, and it's heavily implied their actions give the word its modern linguistic connotations. Recent Doctor Who has teased the idea of revealing the Doctor's real name with the arrival of, River Song, and the return of Gallifrey at Trenzalore, for which the name acted as a password of sorts.
While there's no debate over what to call the Doctor within Doctor Who's narrative, the situation is far more complicated in real life. This debate all stems from the fact that the credits for the first four Doctors (a period of 19 years) all list the character as either "Doctor Who" or "Dr. Who." Further complicating matters was the frequent use of "Doctor Who" as a catchphrase in the show, usually uttered by uninitiated newcomers who were confused at calling the character just "Doctor." Only on sporadic occasions has the Time Lord actually been referred to on-screen as "Doctor Who," and usually only in an implicit sense, such as the Second Doctor signing his name "Dr. W." It's also worth noting that several classic episode titles refer directly to the lead character as "Doctor Who," for example, Jon Pertwee starring in "Doctor Who & The Silurians."
Finally, the debate looked to be settled when Peter Davison's Fifth Doctor was credited simply as "the Doctor," bringing reality and fiction neatly in line. When Doctor Who was restarted in 2005, however, Christopher Eccleston was once again officially listed as "Doctor Who," only for the credits to change back for the David Tennant era and beyond. The constant back-and-forth has opened up the question of whether "Doctor Who" is a valid title for the character or not, plaguing quiz nights across the globe. Matt Smith's Doctor compounded the situation further when his tenure revealed "Doctor Who?" as the oldest question, creating a genuine in-story significance for the phrase for the very first time.
In true Doctor Who style, however, firm answers are hard to come by, meaning both sides can claim some degree of legitimacy. Clearly "the Doctor" is the favored canon term, but if decades of credits say "Doctor Who," there's obviously some weight behind that name also, especially for fans talking about the character in the real world. Perhaps part of the reason behind the usage of "Doctor Who" in some circles (older fans in particular) is that the phrase is more recognizable out of context. Whereas dropping "the Doctor" in a conversation can just as easily mean your local medical practitioner, using "Doctor Who" to refer to Jodie Whittaker's character is a whole lot easier than explaining "the Doctor from Doctor Who."
Doctor Who season 12 premieres January 1st on BBC and BBC America.