Mankind
Pretty much the only native species inhabiting Earth left, the race of mankind is usually perceived as the weakest race despite being the only sentient species from Earth. Of course, that usually makes the other sentient aliens think that their planet is weak too and only useful for harvesting its materials... However, despite being regarded as weak and useless, humans can be very stubborn and resilient when they put their minds to something.
Uh... I think we know too much of this race already, really...
