It's a simple fact of any long-running TV show that many characters will feel like they weren't given the treatment they deserved, and Doctor Who is no exception.
After all, some characters might be there to further the plot in one specific way, before being tossed aside when their usefulness expires. Other characters might be retired due to unforeseen production issues, while some might just be written poorly, failing to meet their true potential during their time on the show.
Whatever the case, Doctor Who contains countless characters who fall into categories like this - characters that, even though they might've been great for the time they were onscreen (whether a brief stint, or a series-spanning recurring gig), ended up feeling underserved, underused, or generally mismanaged.
Now sure, the writers can't knock it out of the park with every single hero, villain, and bizarre alien they create. We get that. But at the same time, it's perfectly reasonable to want more from a certain character, and on that note, these ones definitely felt like they had a lot more juice in the tank...
10. Kate Stewart
It's rare to meet a character who's instantly likeable, but UNIT boss Kate Stewart ticked that box with her debut appearance in Series 7's The Power Of Three.
From here, she popped up a few more times alongside the Eleventh and Twelfth Doctors, before unceremoniously signing off with Series 9's The Zygon Inversion.
This entry goes hand-in-hand with the way UNIT has been treated in the modern era of the show, because, overall, this element of the Whoniverse has been woefully underserved. The Power Of Three showed great promise by re-introducing Kate's UNIT as a more science-led organisation, but this angle was slowly stripped away until the gun-toting goons took centre-stage in that aforementioned Zygon story.
Oh, and then, UNIT was completely shut down by Chris Chibnall, just so he could make a lame joke about Brexit. "Misjudged" doesn't even begin to cover it.
To put it simply, UNIT and Kate deserve better. A character as intelligent and engaging as she is warrants way more respect - especially when you consider that she's the daughter of one of the most important characters in Doctor Who history.
Fortunately though, there is hope. The reason we've put Kate in tenth place is because she's due to return in Survivors Of The Flux, so depending on how she's handled there, we might be able to forgive some of our current complaints!