The Five Doctors is a special feature-length episode of the British science fiction television series Doctor Who, produced in celebration of the programme's 20th anniversary. It had its world premiere in the United States, on the Chicago PBS station WTTW and various other PBS member stations on 23 November 1983,[2] the anniversary date. The episode aired after the conclusion of the 20th season to celebrate the 20th anniversary. Patrick Troughton and Jon Pertwee reprised their roles as the Second and Third Doctors, respectively. Richard Hurndall portrayed the First Doctor, as the character's original actor, William Hartnell, had died since his last appearance on the show ten years previously. Since Tom Baker decided not to appear in this special, footage from the unfinished serial Shada was used to portray the Fourth Doctor. Wikipedia: https://en.wikipedia.org/wiki/The_Five_Doctors (thetvdb.com)