The Wormhole wrote:
Technically, Ainley worked with six of the seven classic era Doctors, since he did have scenes with Troughton and Pertwee in The Five Doctors. He also had scenes with Hurndall as well, though I'm not sure of he counts.
Well, the pedantic answer is that Ainley's Master appeared with all of the first seven Doctors, but only had a proper scene/conversation with six of them (he only gets to hold Troughton's Doctor at gunpoint in a crowd scene) and one of those was being played by Richard Hurndall rather than William Hartnell at the time.
So five proper Doctors, plus two more sort-of.
But some, believe that His Nemesis in The War Games
was a Prototype for The Master, so, you can almost believe Troughton had dealt with him as well (Pertwee knows Delgado in the First appearance, Right?) and obviously, since Hartnell is First, He went to School with The Master, so....if you stretch Canon, you can justify those other two, IMHO
Well, if we're stretching canon (and the earlier post was asking about Master actors working with multiple Doctors so we're stretching topic anyway!)... the Troughton Doctor met the Delgado Master in a book written by a person of this forum... and must have met him for the Master to have a grudge against him when he first turned up during Pertwee's time as mentioned, as you mention, in Terror of the Autons.
But The War Chief from The War Games is not the Master - seeing as Terrance Dicks created the War Chief and co-created the Master and then resurrected the War Chief for one of his books without making him the Master, I think we can take that as definitive!
But it does open up an interesting might-have-been though - Philip Madoc, who played the even nastier War Lord in War Games, did wonder why he wasn't asked back for a rematch, and it would have made a bit of sense to have him return rather than suddenly introducing the Master as this old enemy we'd never seen before. If producer Barry Letts hadn't already had his old friend Roger Delgado in mind to play the new regular villain, then we might perhaps have had Philip Madoc back as the War Lord, "or as he now calls himself, The Master."