Vikram Pandit abruptly stepped down as CEO of Citigroup on Tuesday, shocking Wall Street, after steering the bank through the 2008 financial crisis and the choppy years that followed.

Pandit’s replacement, effective immediately, is Michael Corbat, who had been CEO of Citigroup’s Europe, Middle East and Africa division, the bank said. Corbat has worked at Citi and its predecessors since he graduated from Harvard in 1983, it said.

Pandit will also relinquish his seat on Citi’s board of directors. A second top executive also resigned as part of the shake-up: President and Chief Operating Officer John Havens, who also served as CEO of Citi’s Institutional Client Group.

The move followed a clash with the company’s board over strategy and performance at businesses, including its institutional clients group, The Wall Street Journal reported. Shareholders also have objected to Pandit’s big pay packages. He received $15 million in 2011.

The news came as a surprise, and Citigroup offered no explanation. There was no hint of the departure Monday, when the bank announced strong third-quarter earnings.

In an analyst call that lasted an hour and 40 minutes, and a shorter call with reporters, no one asked bank executives how long Pandit planned to stay, or whether there was a succession plan in place.

The strong quarter sent Citigroup’s stock price to its highest level since early April.

Pandit is credited with slimming the bank by selling businesses, removing it from government ownership after a bailout in 2008 and righting its balance sheet after billions in losses on bad mortgage investments made before he took the helm.

Today, Citi is the country’s third-largest bank, with $1.9 trillion in assets, behind JPMorgan Chase and Bank of America, according to the Federal Reserve.