Harry Sullivan, in most parts of the fandom, gets ignored. Granted, it is a bit understandable; he wasn’t in the TARDIS for long (we never actually see him in the TARDIS, curiously), nor was a he ever a sole companion, but rather part of a three person team tardis. But the thing about Harry is, while he may not have been on the show for long he actually made a mold for the one of the most well-known male companions of New Who, Mickey Smith.
As the above gifs show, the Doctor, while a kind soul, can be a kind of a dick
most some of the time. He does ask Harry aboard, so it does mean that he actually likes Harry enough to want to go travelling with him. That doesn’t mean, however, that he’s always going to be nice to Harry. While Harry can be a little bumbling, he overall has a good heart and is actually quite sharp and clever, picking up on things like how to navigate back to Nerva space station after just seeing the Doctor do it once. The Doctor, however, can be a bit rude and mean, none more apparent than when he calls Harry an imbecile despite making a mistake that anyone else would.
This doesn’t just stop with Four and Harry, though; this can be seen when we first meet Mickey and Nine calls him ‘Mickey the Idiot’ after continually getting Mickey’s name wrong. Why does the Doctor do this? Sure Mickey may be a bit bumbling sometimes, but he also picks up concepts quickly, like when confronted with the overwhelming tension of the Slitheen taking over the world unless he helps hack into secure, private government files; he doesn’t freak out, he rolls with it, just like Harry. So why call him an idiot? Maybe he doesn’t like Mickey’s face. Maybe he just wants Mickey to shove off so he can have Rose to himself. Maybe he really does think of Mickey as an idiot while ignoring other people’s similar mistakes. Either way, both situations show that the Doctor isn’t always the best judge of character, and can also be mean for no apparent reason.
Aside from their unfortunate ability to raise ire in the Doctor, Harry and Mickey also are among the more practical, sensible minded companions on the show. This can be seen in especially in the way they depart from the Doctor. Harry, after getting more than his fair share of adventures, decides that it would be better for him to stay on earth with the UNIT crew. He isn’t tragically separated or unfortunately treated. He just takes stock of his life, where he is at, where he is best needed, what he needs, and leaves. No fuss, just ‘I’ll stay here.’ Mickey, similarly, spends most of his last serial as a companion taking stock of his life and choices, and realizing that maybe a life with the Doctor isn’t what he needs right now. He looks at his life and choices and makes the best decision for himself, like Harry. No fanfare so extreme sadness, just his reasons and a simple good-bye. They both have seen amazing things but they also know when the time is right to say good-bye to those things and think of yourself and your well being first, which is very admirable.
In the end, these two also work as incredibly effective foils for the Doctor. Harry, while smart and quick-witted, is humble and quieter in nature than Four (then again, everyone is quieter and humbler in comparison to Four). Harry’s gentlemanly manner and slight culture shock is in complete contrast to Four’s alien countenance. Mickey makes an even more complex foil; while Nine may be wearing simpler, more work-appropriate clothes and donning a working class accent this regeneration, he is still in sharp contrast to Mickey. Mickey hasn’t put on these working class affectations to escape the memory of his recently-deceased upper class peers like Nine has. Mickey was born, raised, and continues to be working class, while the Doctor can easily slip into (and out of) that particular persona, thanks to his nature as a Time Lord. The Doctor possesses a freedom Mickey (or any human) can’t even touch. Harry shows the strangeness of this new Doctor’s countenance, while Mickey shows the strangeness of the Doctor’s whole persona.
Ultimately, however, these two function most efficeintly to point out the unreliable narration that frames the show. After all, why do we call these two men ‘imbecile’ and ‘idiot’ when clearly they are smart, competent men? Because the Doctor calls them that, and the show never aggressively sets out to question the ruling; the Doctor’s ruling is implied as right, given the lax refuting nature of the show. But given the facts, is his judgement really to be trusted? The Doctor may be a powerful, wise, learned man, but that does not mean he’s always right. This misjudgment of character makes us step back not question not only the Doctor’s smaller judgments but his larger ones, too, such as his role in the Time War.
Harry may have been called an imbecile by the Doctor, but he isn’t that and so much more, too. He is a smart, sensible, humble guy who serves as a great foil to the Doctor, who is incredibly charismatic but vain, judgmental and a touch irrational. And it is his mold that gets picked up again in New Who as he helps show the flaws and failings of the Doctor as a character. The Doctor isn’t a god; he’s just as messed up as humans. And Harry and Mickey aren’t idiotic imbeciles but under-appreciated, kind-hearted men.