Who are the 10 richest Americans?

Sarah Coles

Bill Gates
Bill Gates

The old adage that everything is bigger in America certainly rings true this year. Forbes' list of the richest Americans reveals some astounding fortunes - including the richest man in the world, and a man who added $12.5 billion to his wealth in just one year.

So who are the top ten richest Americans, and how have they made their fortunes?