The serials The Deadly Assassin and Mawdryn Undead and the 1996 TV film would later establish that a Time Lord can only regenerate 12 times, for a total of 13 incarnations. This line became stuck in the public consciousness despite not often being repeated, and was recognised by producers of the show as a plot obstacle for when the show finally had to regenerate the Doctor a thirteenth time. The episode "The Time of the Doctor" depicted the Doctor acquiring a new cycle of regenerations, starting from the Twelfth Doctor, due to the Eleventh Doctor being the product of the Doctor's twelfth regeneration from his original set.
What was Time Lord's career?