Dougan took over Credit Suisse in 2007, just in time to catch the worst global financial crisis in decades. 

Last year Swiss lawmakers started pressuring him to resign after the bank plead guilty to helping clients evade taxes. The $2.6 billion fine the bank had to pay resulted in its first quarterly loss since 2008.

Pressure was mounting on Dougan from inside the bank too. After he testified on Capitol Hill about the tax evasion matter, a staff group representing Swiss bankers at Credit Suisse and other Swiss banks demanded that he apologize. They said Dougan's testimony simply served to "vilify lots of employees that had nothing to do with offshore U.S. banking."

Thiam, for his part, has never worked in banking.