6. 'Human Nature' Characters
Remember the thing about personal canon when it comes to Doctor Who? Well, the Paul Cornell story Human Nature is possibly the best example of why this is the least brain-aching approach to take. Originally released in 1995 as a Seventh Doctor novel for the Virgin New Adventures series, the story was so popular that it was adapted for the modern show under the Tenth Doctor. While the story contains some major differences, like the Seventh Doctor turning human via alien technology he'd acquired whereas the Tenth Doctor had the means aboard the TARDIS already, some of the lucky novel's characters also made the transition. There's the Doctor's human alter-ego John Smith, of course, and Nurse Joan Redfern, played on television by Jessica Hynes, also crosses over from the novel to the television story. She's practically identical to her televised successor, too, as she is widowed before falling in love with Smith. Similarly, a boy in the novel called Timothy Dean, who finds a device holding the Doctor's biodata and starts exhibiting Time Lord abilities, is obviously the basis for Timothy Latimer in the Human Nature/Family of Blood two-parter. There's also Mr Rocastle, the school's headmaster, and the creepy girl with the red balloon. Again, they're not the same characters in any contiguous sense, but Cornell reworked the characters and concepts for a TV audience and made them definitive canon. It's up to your own judgement if these two suspiciously similar events took place twice in the Doctor's life, just once... or not at all. If you want the "better" version in your personal canon, you'll have a hard time deciding which one that is. Because of the limitations in each format, both have comparatively stronger and weaker elements, whilst major plot deviations and the fact that they both have the same writer makes it hard to determine which is the objectively superior version. So take your pick.