Fueled 1980s buyout craze with junk bonds, padded fortunes of The Forbes 400: Carl Icahn, Ted Turner, Ronald Perelman, Henry Kravis. Pleaded guilty to 6 counts of security fraud in 1990. Served 22 months. Invested in education outfit K12. Longtime philanthropist has donated more than $1 billion to medical causes: melanoma, AIDS, leukemia, breast cancer, prostate cancer, Alzheimer's.