No. 10 -- Patrick Soon-Shiong, Abraxis Biosciences Founder

NET WORTH: $5.6 billion

Warren Buffett often speaks of the dumb luck of being a billionaire, and the "ovarian lottery" of being born in the right place at the right time. Soon-Shiong was born to Chinese immigrants who fled the country during World War II for South Africa. He is the only American citizen on the Buffett/Gates list born outside the country.

Soon-Shiong was one of the first non-white surgical residents at Johannesburg's General Hospital.

As Forbes said of the drug king in its review of the Richest Americans: "Dr. Patrick Soon-Shiong has been called ruthless and a headline-grabber. As a scientist he has been criticized for hyping his research results; as a drugmaker he has been accused of ripping off investors. Short-sellers have boldly bet against him, risking huge losses. Even his own brother, an early backer, sued him for fraud and fired him -- twice -- from the company they started. Their skirmishing lasted two years and destroyed their relationship."

In this case, Soon-Shiong has grabbed a good headline. In a letter explaining his decision to join the major donors, he wrote, "Growing up in South Africa during the time of apartheid, we had direct experience of inequality, including great disparities in health and access to good care. After thirty years living in the United States, we see similar disparities in health care on our doorstep in Los Angeles, and across the nation. What was unconscionable to us in South Africa in the twentieth century is just as unconscionable in the United States in the twenty-first."

It should be noted that just because some notable American billionaires aren't on the Buffett/Gates list doesn't mean they are unconscionably greedy individuals. Google founders Larry Page and Sergey Brin have promised to make a social impact that will "eclipse Google itself" and in 2005, outlined plans for Google.org, a charitable foundation and social investing network. Likewise, David Koch has made the top of lists of the country's biggest givers, including placement on BusinessWeek's 50 Top American Givers, and it's a list in which the Walton family has also been featured.

And while it's good to line up the hedge fund and biotech donors, they may need to spend some more time dialing Bentonville, Arkansas: The biggest problem for Buffett and Gates in lining up the Top 10 Richest Americans is Wal-Mart ( WMT). Four members of the Walton clan are among the Top 10 Richest Americans, according to Forbes -- spots four through eight on the list, with assets ranging from $19 billion to $23 billion -- but not one of them is on the Giving Pledge list.

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