Bill Mills, the long-term Citigroup veteran who has been parachuted back to his old role of running Europe, led the bank’s expansion into Russia and eastern Europe during a previous stint as regional head.

Mills, an investment banker, will also remain in his current role of chief executive officer of North America, a newly created position he took up at beginning of this year after a management reshuffle. He was previously appointed head of Citi's European business in 2008.