I have a feeling Oswin is going to end up something like Scaroth (though not alien I just mean time fragmented.)
That was my favourite speculation, posted also a page or two back. It made me think about something, too…
It seems like a bunch of alien antagonists are directly responsible for either the creation or the development of the Human civilization.
The Silence have been present since Humanity's beginning, molding their development.
Scaroth, a Jagaroth who crashed on Earth hundreds of millions of years ago, accidentally created life on the planet and then molded Humanity's development at several points in history (giving them the secret of fire and astronomy, for instances).
The Racnoss Empress
triggered the creation of the Earth in order to become its core. That's fairly crucial to Humanity's development.
The Monk, a Gallifreyan, was responsible for the creation of Stonehenge (this creation may have also been assisted in some way by the Alliance… er, if they ever existed in the first place!). He also influenced Leonardo da Vinci, who himself was a strong influence on the progression of Western civilization.
How many other "bad guys" had the side effect of actually making us what we are today? Anybody got more for the list?
Side note: I'm surprised that the Silence and Scaroth never butted heads. Or maybe they did. But wouldn't they want to stop his plan of unmaking Humanity?
edit: I also vaguely recall an antagonist that "tested" humanity every few years and had finally found it wanting (thus eligible for destruction) when the Doctor coincidentally popped by. Which ep was that? (editedit: I might be thinking of the Dæmons)
edit: I thought that Fenric might qualify, but it looks like he largely did inconsequential things.
edit: Ah, the
Fendahl molded humanity to fit their needs, as well. Ye gods, it's too bad we never got a big throwdown between all these races considering that they were pretty much at odds in intent for millions of years on the planet!