Probably those people who walked here from Europe some 10 to 13 thousand years ago over the land bridge. Only it wasn't called America then. Although I believe fossils of people have been found in the usa dating back to around 50 thousand years.
Well, as other answers clearly state, the Native Americans were here first. The first Europeans to arrive on the shores of the Americas were (Guess what? It isn't Columbus!) the Norse (Vikings). There is also evidence that the Templars may have come here, as well, before Columbus 'discovered' the Americas. Some historians believe the Holy Grail is hidden somewhere in North America. Columbus was just the first person to make his discovery of the Americas known, and he never once set foot on the mainland of North or South America.
The indians were the first here til the Europeans came over here and k i l l ed them off with their weapons and diseases. After The Indians gave them food and help them they k i ll ed them same with the Africans.