How did he make his billions? A partner at Salomon Brothers, he was fired when it was bought out in 1981. But he used his $10m pay-off to set up a firm providing banks with real-time information about the world's trading floors. Bloomberg has since diversified, and the newswire services have made him a global media magnate. He has even profited from the recession: as the markets tanked, the demand for his data soared, and he made $4.5bn.
The secret of his success? Opportunism. A lifelong Democrat, he joined the Republicans to win the 2001 mayoral election, but became an independent when Bush's ratings fell. Late last year, he engineered a change in the law so that he could run for a third term. A financial crisis needs a financial expert in charge, he said.