You can find a lot of crazy stuff by mining the depths of classic Doctor Who episodes, including some stuff that defies the show's canon. These days we know 11 official incarnations of our favorite Time Lord, but in a 1976 episode it was revealed that by the Tom Baker era our Doctor had already regenerated several more times than we'd seen on screen.
Up until this episode aired, most Doctor Who fans were probably just like us: They assumed that the Doctor's first incarnation was the first one they'd seen, played by William Hartnell beginning in 1963. But in "The Brain of Morbius" in the show's 13th season, quite a few other Doctors popped up.
Morbius was a criminal from Gallifrey who'd somehow been reduced to little more than a brain in a very messily constructed body. When the Doctor challenged him, the two settled the matter not with violence, but with a brain duel, plugging their heads into some kind of machine to see who had the superior mind. This triggered the revelation that the Doctor wasn't on his fourth incarnation, but on his 11th.
Watch the video at about the 14-minute mark to see it happen. The space in between the two brain duelers is filled with images of past Doctors as the battle goes on. At first you see only recognizable faces: Third Doctor Jon Pertwee, Second Doctor Patrick Troughton and First Doctor Hartnell. But then you start to see some unfamiliar identities for the Doctor, which apparently were portrayed by crew members George Gallacio, Robert Holmes, Graeme Harper, Douglas Camfield, Philip Hinchcliffe, Christopher Baker, Robert Banks Stewart and Christopher Barry.
This became problematic later when the Who writers established that Time Lords have a 13-regeneration limit. If you counted these eight previously unseen Time Lord incarnations, that would mean that Baker wasn't the Fourth Doctor, but the Twelfth, and the series had to end with canonical Fifth Doctor Peter Davison, and that just wouldn't do. So the "Brain of Morbius" sequence was forgotten, and these days it's remembered by only the die-hard Baker fans.
The 13-regeneration rule has since become a bit loose in the Doctor Who mythos, so we could theoretically count these guys as Doctors again. At least then he could say he's had a beard at some point.
(via Mental Floss)