Planes would be good too. But when I mean aliens, I do mean other planets. Stuff in the same dimension and universe, but from different places. Usually different biology too.
I was born human. Flesh and blood and all of that. Then the thing happened and I ended up amongst a bunch of duplicates without them realizing it later on in a copy of my body. The thing was alien though, so anything it made would technically be alien too.
Still the same person, all the memories and feelings, The Doctor checked.