Unfortunately, the name of their planet of origin (in Star Wars) has been lost to time. Humans have leading members of the Galactic scene for a long period also, perhaps simply because of numbers. Humans were among the founding species of the Republic.
During this period, humans gained much power in the fact that the Republic's armies were made up of Clones of a Mandalorian Human, and were therefore essentially Human.
They held positions in the Republic's senate up until its disbandment by the Supreme Chancellor. After the Republic's collapse at the hands of the Supreme Chancellor, Humans continued to hold much power, politically and militarily, but this time, it was near-absolute power because of the Empire's Humanist policies.
The Empire's prejudices is most of the reason the GCW started, as many species could no longer take the Empire putting them down, purely for Speciest (similar to Racist, but on a grander scale) reasons. Many humans also rebelled, as they either could not take the Empire treating other species as terribly as it was.