Warren Buffett: $60.8 billion

The Oracle of Omaha, as he's known for the way his every investment decision is followed by thousands. He began investing as a teenager in the '40s and gradually grew his firm, Berkshire Hathaway. Buffett, 86, is notoriously frugal personally and favors investing in companies with proven business models over new industries, such as in technology. He's said he will give away the bulk of his wealth to philanthropy and since 2006 has been donating blocks of Berkshire stock to the Bill and Melinda Gates Foundation.