William Joseph Mills is a businessperson who has been at the helm of 6 different companies is Chief Executive Officer-North America at Citigroup, Inc. and on the board of 6 other companies.

In the past he occupied the position of Vice President of Standard & Poor's Corp., Chairman & Chief Executive Officer of Citibank International Ltd., Chairman & Chief Executive Officer of Citigroup Global Markets Europe Ltd., Chief Executive Officer at Citigroup Global Markets Ltd. (Market-Maker), Head of Corporate & Investment Banking at Citigroup Global Markets Ltd., Chief Executive Officer EMEA at Citigroup Global Markets (Pty) Ltd., Co-Head-Investment Banking Division at Salomon Smith Barney, Inc. and Co-Chairman of Business Council for International Understanding.

William Joseph Mills received an undergraduate degree from Denison University.