"The Oracle of Omaha," as Warren Buffett is sometimes known, has won public affection for his folksy, genial and trenchant observations on investing.

His frequent pronouncements about the state of American business typically are taken at face value by the media and regulators, in part because of Buffett's reputation for integrity.

He became known as a governance guru in 1991, after stepping to the helm of a foundering investment bank, Salomon Brothers. Buffett saved the bank and became a business hero.

He cemented his reputation for civic-mindedness in 2006 when he committed most of his personal fortune to the Bill & Melinda Gates Foundation. In 2007, Buffett scolded the government for creating a system that gave him a lower tax rate than his secretary, who earned $60,000 a year.

Buffett's lustrous reputation recently has been tarnished, however. In 2007, human-rights advocates challenged Berkshire's multibillion-dollar holdings in a Chinese oil company with close ties to the Sudanese government, which is blamed for atrocities in Darfur.

Buffett rejected accusations that he profited from the company, PetroChina. A few months later, he sold the holdings at a profit.

Despite Buffett's advocacy of good practices by corporate boards, at 78, he hasn't named a successor to head Omaha-based Berkshire, which remains deeply dependent on his investing acumen.