The American stereotype?

This is just a short question, but what Stereotype does the world place on America or American people themselves? And what causes this stereotype to happen? I believe it began when foreigners had encounters with Americans which happened to be unintelligent, or possibly some kind of statistic. I asked my mom and she always replies with "they're just jealous of us" but i strongly disagree. Is the stereotype formed of jealousy or something else? I have been wondering this for a long time.