Steven Moffat has described the Twelfth Doctor as a fiercer incarnation, a more alien one. Now, we naturally expect each Doctor to contrast with the last. That saidthe last time we got a fiercer, more alien Doctor, the results weremixed. If by mixed, you mean cancelled. Colin Baker was hamstrung by issues outside of his control, but there are still parallels between him and Capaldi. Baker was older than his predecessor, who at the time was the youngest ever Doctor. Baker inherited a companion. And Baker, as might be the case with Capaldi, portrayed a frighteningly unpredictable Doctor. This didnt work particularly well in the 80s- introducing your leading man by having him strangle a helpless young woman usually doesnt- so what are the chances for todays production team? While it seems unlikely theyll commit a gaffe that show-killing, the contrast between Capaldi and Matt Smith will be measured by his relationship with the companion. If Moffat misjudges this, hell alienate those fans for whom Clara is their window into the Whoniverse. And if history is any guide, it would take over a decade in the wilderness and a fully blown reboot to get them back