I love this scene to pieces. It’s just seconds long and it’s one of my favorite scenes in the black and white era. The Doctor and the War Chief make eye contact… and they recognize each other. Of course, we had to underline what makes this important to our son, without giving anything away. He doesn’t quite grasp the ramifications. Neither did many of the people watching, perhaps.
Four years previously, when William Hartnell was the star, the Doctor had met another of his people. Played by the popular comedian Peter Butterworth, he called himself the Monk, had his own TARDIS, and, perhaps remarkably, was the only individual villain in the show’s first six seasons to get a rematch with the Doctor. He originally appeared in a four-part serial in July 1965, and then came back in January for three weeks as an ally of the Daleks, but the character was not used again after that. That’s in part because Butterworth became very busy making Carry On movies, and in part because the constantly changing production teams of Who during these days probably wanted to do their own things. The Monk was later resurrected in comics, novels, and audio adventures. I was pleasantly surprised to learn that Graeme Garden occasionally plays the character opposite Paul McGann’s Eighth Doctor in radio/CD stories.
But for the entire tenure of Patrick Troughton’s time as the Doctor, there’s been no hint of any other time travelers at all other than the Daleks, no other TARDIS, and certainly no people from his past who might recognize him*. There’s a great bit early on in this episode where the Doctor gets a bad feeling that he knows where this technology came from, but declines to elaborate to Zoe. Suddenly it becomes very clear that he’s going to have to start elaborating before this adventure ends.