While struggling with his past regenerations, the Doctor's Ganger alludes to several previous Doctors' words.
On a few occasions, previous Doctors have returned to the role, guest-starring with the incumbent:
During the sequence in which the Doctor's brain is scanned, images of all the previous Doctors and most of his former companions appear on a screen.
In order to complete the test, the player must use information from previous Doctor Who tie-in websites.
He was never fully accepted by the collective consciousness of the previous Doctors nor did he want to be.
The previous Doctor had died.
In her introduction, Martha is represented as being 'normal' in ways previous Doctor Who companions were not.
These preparations were heard in four previous Doctor Who audio stories.
Russell T Davies characterised the character as a "stripped down" version of previous Doctors.
The previous seven Doctors appear in the time machine's mirrors.
