S&P says Deven Sharma will be replaced by Douglas Peterson, now the chief operating officer of Citibank N.A., Citigroup's chief banking arm.
The agency says Sharma decided to move on after helping S&P separate its data, pricing and analytics business from its ratings business, a restructuring announced late last year.
Its statement makes no mention of the downgrade that sent shock waves through global financial markets and was sharply criticized by the Obama administration, which said the agency's analysis was fundamentally flawed.
