Sam Walton started poor as a Depression-era baby in Oklahoma's dust bowl. But he eventually became the richest man in the nation, building his chain of Wal-Mart stores into the world's largest retailer. Interviews with associates, including former Wal-Mart board member Hillary Rodham Clinton and ex-CEO David Glass, detail Walton's strategy and trace his incredible road to success. Family members, including his wife and son, also offer insights.