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Some of the stories during the Seventh Doctor's tenure, part of the so-called "[[Cartmel Masterplan]]", were intended to deal with this issue by suggesting that much of what was believed about the Doctor was wrong and that he was a far more powerful and mysterious figure than previously thought. In both an untelevised scene in ''[[Remembrance of the Daleks]]'' and the subsequent ''[[Silver Nemesis]]'' it was implied that the Doctor was "more than just another Time Lord". The suspension of the series in 1989 means that none of these hints were ever resolved. The "Masterplan" was used as a guide for the [[Virgin New Adventures]] series of novels featuring the Seventh Doctor, and the revelations about the Doctor's origins were written into the novel ''[[Lungbarrow]]'' by [[Marc Platt]]. However, the [[Whoniverse#Inclusion and continuity|canonicity]] of these novels, like all [[Doctor Who spin-offs]], is open to interpretation.
==When incarnations meet==
Due to time travel, it is possible for the Doctor's various incarnations to encounter and interact with each other, although this is supposed to be prohibited by the First Law of Time (as stated in ''[[The Three Doctors (Doctor Who)|The Three Doctors]]'') or permitted only in the "gravest of emergencies" (''[[The Five Doctors]]''). In the 1963–1989 television series, such encounters were seen on three occasions, in ''The Three Doctors'' (1972), ''The Five Doctors'' (1983) and ''[[The Two Doctors]]'' (1985). In ''[[Day of the Daleks]]'' (1972), the Third Doctor and [[Jo Grant]] very briefly met their future selves due to a glitch during a temporal experiment (the serial was supposed to end with the same scene depicted from the perspective of the "other" Doctor and Jo, but was excised because it was anticlimactic<ref>[[Andrew Pixley (historian)|Pixley, Andrew]], "The DWM Archive: ''The Day of the Daleks''", ''[[Doctor Who Magazine]]'', #501, 7 March 2001, p.31 (sidebar: "Editing Episode Four").</ref>). In "[[Father's Day (Doctor Who)|Father's Day]]" (2005), the Ninth Doctor and Rose observed but did not interact with past versions of themselves; when Rose changed history, the earlier selves – after momentarily noticing Rose running past – vanished and a temporal paradox was created that attracted the extradimensional [[List of Doctor Who monsters and aliens#Reaper|Reapers]]. The Tenth and Fifth Doctors met in the TARDIS in the mini-episode "[[Time Crash]]", which aired on 16 November 2007 as part of the BBC's annual [[Children in Need]] appeal. This marks the only time the Doctor has met a previous incarnation since the show's revival. Although the scene aired outside the series itself, it was established as taking place between the events of "[[Last of the Time Lords]]" and "[[Voyage of the Damned (Doctor Who)|Voyage of the Damned]]."
The BBC novel ''[[The Eight Doctors]]'' was written by respected Doctor Who writer [[Terrance Dicks]], the same author who wrote ''[[The Five Doctors]]''. In it, he tries to reconcile the continuity errors of the 1996 movie, while having the Eighth Doctor meet and interact with each of his previous selves.
Physical contact between two versions of the same person can lead to an energy discharge that shorts out the "time differential". This is apparently due to a principle known as the [[Blinovitch Limitation Effect]], and was seen when the past and future versions of [[Brigadier Lethbridge-Stewart]] touched hands in ''Mawdryn Undead''. Oddly, the Doctor's incarnations do not appear to suffer this effect when encountering each other and shaking hands. This has never been explained. An essay in the ''About Time'' series by [[Lawrence Miles]] and [[Tat Wood]] suggests that Time Lords are somehow exempt from the effect by their very nature. [[Rose Tyler]] is seen holding an infant version of herself in "Father's Day", with no visible energy discharge, but the contact does allow the Reapers to enter the church in which the Doctor and several others are taking refuge. While doing a live commentary on the episode at the 2006 Bristol [[Comic Expo]], episode author [[Paul Cornell]] said that this is supposed to be due to the Blinovitch Limitation Effect, even though it is not mentioned by name. He also suggested that the lack of a spark may be down to the fact that the Time Lords were no longer around to manage anomalies.
The interaction of the Doctor's various incarnations produces a continuity anomaly that requires [[suspension of disbelief]] on the part of viewers, as one may assume that his past selves would forget that he would later regenerate. In ''[[Castrovalva (Doctor Who)|Castrovalva]]'', the newly-regenerated Fifth Doctor clearly indicates that the outcome of his regeneration cannot be predicted; however, the Fifth Doctor should have had memories from his earlier incarnations of having met himself per the events of ''The Two Doctors'' and ''The Five Doctors''. Also, the Second, Third and Fifth Doctors should be already familiar with the events of ''The Five Doctors'', having already lived through them multiple times. It has been suggested in fandom that the Time Lords erase the Doctor's memory after such encounters (and in ''The Two Doctors'' there is mention of Dastari administering to the Second Doctor a drug that he bemoans "affects the memory"); the novel ''[[The Empire of Glass]]'' features the First Doctor directly after his return from the events of ''The Three Doctors'', his memory of the adventure having been totally erased barring a vague recollection of meeting "a [[Third Doctor|dandy]] and a [[Second Doctor|clown]]". The [[Virgin Missing Adventures]] novel ''[[Cold Fusion (Doctor Who)|Cold Fusion]]'' by [[Lance Parkin]] suggests that memory-erasure is sometimes, but not always, due to something called "Blinovitch Conservation".
In the 2006 episode "[[School Reunion (Doctor Who)|School Reunion]]", the Tenth Doctor and Sarah Jane Smith both seem to indicate in dialogue that they haven't seen each other since her departure from the TARDIS in ''[[The Hand of Fear]]'', although this contradicts their having met later during ''The Five Doctors''. She, in that story, does not realise that the [[Fifth Doctor]] is a later incarnation of the [[Third Doctor|third]] and [[Fourth Doctor|fourth]] Doctors with whom she had previously travelled. In "Time Crash", the Tenth Doctor remembers and reproduces what he saw himself do when he was the Fifth Doctor, a fact that seems to surprise the Fifth Doctor himself.
Russell T Davies has expressed a dislike for stories in which multiple incarnations of the Doctor meet, stating that he believes they focus more on the actors than on the story itself.<ref name="rtd">{{cite news| first=Cameron| last=Robertson| url=http://www.mirror.co.uk/news/tm_objectid=16926209&method=full&siteid=94762&headline=writer-russell-won-t-be-asking-old-docs-back--name_page.html| title=Writer Russell won't be asking old Docs back|work=The Daily Mirror |___location=UK| date=10 April 2006| accessdate=13 April 2006
}}</ref> David Tennant had shown enthusiasm for the idea of a multi-Doctor story, but has expressed doubts about the practicality of shows involving multiple previous Doctors, given that three of the actors who played the character are now deceased.<ref>{{cite news| last = Ben| first = Rawson-Jones| title = Tennant talks about multiple Doctor story| work=Cult – News| publisher=[[Digital Spy]]| date = 23 March 2007| url = http://www.digitalspy.co.uk/cult/a44303/tennant-talks-about-multiple-doctor-story.html| accessdate = 26 March 2007 }}</ref>
Since the series revival, there has been one multi-Doctor story, the Children in Need special ''[[Time Crash]]''. Before that, the only references to past incarnations (from 1963 to 1996) have been in the aforementioned episode "School Reunion" (in which the Doctor acknowledges having regenerated "half a dozen times" since [[The Hand of Fear|last seeing Sarah Jane]]) and in drawings that the Doctor (who has temporarily become human to hide from the Family Of Blood) makes based on dreams of his other life in the 2007 episode "[[Human Nature (Doctor Who episode)|Human Nature]]". Seen on screen are the First, Fifth, Sixth, Seventh and Eighth Doctors, but a fuller view briefly available on the BBC website depicted all ten incarnations. However in the 2008 Christmas episode, [[The Next Doctor]], the Tenth Doctor discovers an info stamp originally held by the Cybermen, which includes images of all his past selves. This is a clear affirmation of his past, and that the (then) current incarnation was indeed the [[Tenth Doctor|Tenth]]. This was reaffirmed in the episode "[[The Eleventh Hour (Doctor Who)|The Eleventh Hour]]", when the Doctor asks the Atraxi whether this planet is protected. The Atraxi then shows 10 images, one of each Doctor from the first to the tenth, with the eleventh walking through the image of the tenth at the end. This is also confirmed in the episode "[[The Lodger (Doctor Who)|The Lodger]]", when the Doctor, explaining to Craig who and what he is, points at his face and says, "Eleventh."
Because each new Doctor is different from his previous incarnations, how their personalities interact varies when two or more different incarnations encounter each other. ''Time Crash'' featured [[Peter Davison]] returning as the Fifth Doctor. This event is explained as occurring due to the current Doctor having left his shields down when rebuilding the TARDIS following "[[Last of the Time Lords]]" and then accidentally crossing the Fifth Doctor's timeline, allowing the two TARDISes to merge. When the Tenth Doctor effortlessly averts the impending Belgium-sized hole in the Universe caused by this temporal anomaly, he reveals having known what to do because he saw himself do it as the Fifth Doctor and remembered. He goes on to tell the Fifth Doctor how fond he was of his incarnation and how he influences the current Doctor's personality.<ref>{{cite news
| first =
| title = Dr. Peter is Back in the TARDIS
|work=The Sun |___location=UK
| date = 21 August 2007
| url = http://www.thesun.co.uk/sol/homepage/showbiz/tv/article265299.ece
| accessdate = 16 October 2007 }}<br />{{cite news
| first =
| title = Peter is Doctor Grew
|work=The Sun |___location=UK
| date = 13 October 2007
| url = http://www.thesun.co.uk/sol/homepage/showbiz/tv/article337262.ece
| accessdate = 16 October 2007 }}</ref> However, in their two meetings, the [[Second Doctor]] and [[Third Doctor]] had a degree of antagonism towards each other, with the patriarchal [[First Doctor]] critical of them both. During the [[Virgin New Adventures]], the Seventh Doctor was occasionally at odds with his subconscious memory of his previous incarnation as his memory of his past self became increasingly associated with the [[Valeyard]], his dark future self, but he eventually accepted his dark side and 'reformed' his memory of his former self, although it was never established how the two Doctors would interact if they had met in person.
===Reprising the role===
On a few occasions, previous Doctors have returned to the role, guest-starring with the incumbent:
*[[William Hartnell]] and [[Patrick Troughton]] with [[Jon Pertwee]] in ''[[The Three Doctors (Doctor Who)|The Three Doctors]]''. Originally Hartnell's role had been intended to be more extensive, but his health had deteriorated to the extent that he could only make a limited appearance. In the end, it turned out to be his last television role.
*Troughton and Pertwee with [[Peter Davison]] in ''[[The Five Doctors]]'', the twentieth anniversary special, with another actor, [[Richard Hurndall]], standing in for the late William Hartnell (the story began with a clip from ''[[The Dalek Invasion of Earth]]'' featuring Hartnell himself). [[Tom Baker]] declined to appear, feeling that the role came too soon after he had left the programme (a decision he later said he regretted<ref>''The Tom Baker Years</ref>) and the narrative was reworked to use clips from ''[[Shada]]'', an intended six-part story from the Fourth Doctor's era that was never completed due to industrial action. A waxwork dummy of Baker from [[Madame Tussauds]] was used in the publicity photographs.
*Patrick Troughton with [[Colin Baker]] in ''[[The Two Doctors]]''.
*Jon Pertwee, Tom Baker, Peter Davison, Colin Baker, and [[Sylvester McCoy]] – with rubber dummy heads standing in for the late William Hartnell and the late Patrick Troughton—in ''[[Dimensions in Time]]'', a charity special in aid of [[Children in Need]] in 1993, the programme's 30th anniversary year. Except for the [[mannequin]] versions of Hartnell and Troughton, no two Doctors are shown on screen at the same time. (This story was a crossover with ''[[EastEnders]]'').
*Peter Davison, Colin Baker and Sylvester McCoy in the first Big Finish audio adventure, ''[[The Sirens of Time]]''.
*Peter Davison, Colin Baker, Sylvester McCoy and [[Paul McGann]]- the first three appearing initially as holograms using the Doctors' appearances and later as the [[Eighth Doctor]]'s subconscious memory of his past selves), with Jon Pertwee posthumously joining them by virtue of an extant fan recording, in the [[Big Finish Productions|audio]] adventure ''[[Zagreus (Doctor Who)|Zagreus]]'', a fortieth anniversary special and the fiftieth release.
*Colin Baker and Sylvester McCoy in the second half of the audio ''[[Project Lazarus]]'' (Although the Sixth Doctor in this story is later revealed to be a [[cloning|clone]] of the Sixth Doctor created from DNA samples extracted during his previous visit rather than the actual Sixth Doctor).
*Peter Davison with [[David Tennant]] in the 2007 [[Children in Need]] special "[[Time Crash]]".
*Peter Davison, Colin Baker, Sylvester McCoy and Paul McGann in the Big Finish Audio ''[[The Four Doctors]]''.
Other actors have portrayed the character of the Doctor outside of the television series. For details on this see under [[Doctor Who#Adaptations and other appearances|Adaptations and other appearances]] in the main article and [[Doctor Who spin-offs|''Doctor Who'' spin-offs]].
For a list of all actors who have played the Doctor see [[List of actors who have played the Doctor]].
==Relazioni sentimentali==
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