Vikram Pandit, who steered Citigroup through the 2008 financial crisis and the choppy years that followed, abruptly left the bank on Tuesday, stepping down as CEO and as a director.

The move shocked Wall Street, and Citigroup offered no explanation. There had been no hint of the departure Monday, when the bank discussed its strong third-quarter earnings in lengthy calls with analysts and reporters.

A second top executive resigned as part of the shake-up: President and Chief Operating Officer John Havens, who was also CEO of Citi's Institutional Client Group, which serves global companies, banks and governments.