David Olson, the former head of credit trading for JPMorgan Chase & Co.'s chief investment office in North America, joined Citigroup Inc.'s bond-trading unit, according to people familiar with the matter.

Olson started yesterday and reports to David Cohen, head of investment-grade bond trading for New York-based Citigroup in North America, according to the people, who asked not to be named because the matter isn't public. He will run the hybrids and preferred securities trading desk.

Olson, a former U.S. Navy nuclear submarine pilot, left JPMorgan in December, about five months before the bank disclosed at least $2 billion in losses from the CIO's London operation. JPMorgan Chief Executive Officer Jamie Dimon pushed the unit to seek profits by speculating on higher-yield assets such as credit derivatives before the bets soured, according to executives who used to work at the company. Olson's former colleague in London, Bruno Iksil, is known as the London Whale because his bets were so large.

In 2008, JPMorgan's CIO lost $1 billion on securities tied to Fannie Mae and Freddie Mac when the government-backed mortgage agencies were put into conservatorship. Olson has said the only reason he wasn't fired at the time was because Dimon had been "intimately familiar with those positions."

Olson joins Citigroup's credit-trading team as the firm grapples with the European sovereign debt crisis. Chief Executive Officer Vikram Pandit shook up the unit in January, causing senior debt traders Rohit Bansal and Chris Yanney to leave the bank, the third-biggest in the U.S.

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