HONG KONG — Just five years ago, Zhang Yin and her husband were driving around the United States in a used Dodge Caravan minivan, begging garbage dumps to give them their scrap paper.

She and her husband, who was trained as a dentist, had formed a company in the 1990s to collect paper for recycling and ship it to China. It was a step up from life in Hong Kong, where she had opened a paper-trading company with $3,800 to cash in on China's chronic paper shortages.

"I remember what a man in the business told me back then," Zhang Yin said. "He said, 'Waste paper is like a forest. Paper recycles itself, generation after generation.'"

Zhang took that memory all the way to the bank. As a result of her entrepreneurship, she is now richer than virtually any other woman anywhere in the world, including Oprah Winfrey, Martha Stewart, and the chief executive of eBay, Meg Whitman. Her personal wealth is estimated at $1.5 billion or more.