I gather from your other comments that you don't like Harry Sullivan, and I used to love Harry Sullivan, but I also mostly watched 4 as a tween and as a tween I had questionable taste. My strongest memory of him is not any episode he was in, but an idea I had for a M*A*S*H/Doctor Who crossover. (I was watching a lot of both shows at the time, although I had not yet discovered fanfic or online fandom, so alas I never shared the details of this crossover with the world, and the details are long lost.)