"-10" was the caption of a framed picture of a man, which an exhausted Peri Brown once glimpsed while climbing a punishingly long staircase inside the Doctor's TARDIS, alongside several others like it.
The man identified as "-10" was round-faced and nearly bald, with a large nose and ears. A question mark was drawn over his face. (COMIC: Enlightenment)
Behind the scenes
- As portraits labeled "No. 1" and "No. 2", appearing in the background of the same story, are clearly depictions of the First and Second Doctors, readers are led to the assumption that the other individuals in numbered portraits are other incarnations of the Doctor. In the cases of both "-10" and "-6", the "minus" would imply they are in fact incarnations of the Doctor from before the First Doctor — although there is no hard confirmation that the portraits depict the Doctor at all in-story, or indeed, even if they do, that they are accurate.