This is an interesting one. The Doctor has made many friends from across the galaxies over half a century flitting into their lives, sorting them out and disappearing again.
One place he visited twice, fifty years apart, is Peladon, a society which needed to ditch some of its outdated traditions and get with the times – with powerful vested interests holding back any change. Sound familiar? Jon Pertwee’s Doctor visited twice. On his first trip, he helped a new King uncover the dastardly deeds of his advisers. On his second, it was Sarah Jane Smith who injected some feminism into that King’s daughter. Queen Thalira had assumed the throne and the men around her had assumed that they would just rule and she would sit there and look pretty. Sarah Jane encouraged her to be more assertive. Ok, so she didn’t encourage her to create a Parliament and make Peladon a republic, but we can’t have everything.
Oh, and these stories feature the Ice Warriors, now respected members of a Galactic Federation.
There are plenty others I could mention: Banikafalata from the Voyage of the Damned. Astrid Peth from the same episode. The Face of Boe, although you never know, he may be human after all. That lovely beast who saved the earth and was tortured for its efforts until the Doctor and Amy put a stop to that. The Sontaran Strax, shamefully bullied by the Doctor in the Christmas special recently. Madam Vastra doesn’t count because she’s an indigenous inhabitant of earth, but I’m sure she will feature in a future day of the challenge. I mean, that line “I am a lizard woman from the dawn of time and this is my wife” has to be one of the best lines ever.
I think the one I’m going to choose, though, is Jabe from the Forest of Cheem, seen in The End of the World. She shows a lot of understanding, compassion and loyalty towards the Doctor. Sadly, this turns into yet another female character sacrificing themselves for him, but I liked her.