Predicting further fallout in financial markets; says writedowns from credit losses could reach $1.6 trillion. Jazz musician's son executed first trade at age 12. Studied finance at Long Island U., went to work in commodities division of Merrill Lynch 1972. Harvard M.B.A. 1973. Traded futures at brokerage CBWL-Hayden Stone. Feuded with boss, founded Bridgewater Associates at age 25. Today manages $150 billion—including billions in hedge fund assets. Pulling for McCain; has raised thousands of dollars for the presidential candidate.