It's mostly the Doctor and companions dealing with the people of the time period and location. I the only aliens in the past that I can think about was one in which the Doctor came across another Timelord disguised as a monk who wanted to change the history of England regarding the viking raids.

whomod said: I generally don't like it when people decide to play by the rules against people who don't play by the rules.
It tends to put you immediately at a disadvantage and IMO is a sign of true weakness.
This is true both in politics and on the internet."

Our Friendly Neighborhood Ray-man said: "no, the doctor's right. besides, he has seniority."