Standard & Poor's, the ratings company that downgraded the U.S. AAA credit ranking for the first time, will replace President Deven Sharma with Citibank NA Chief Operating Officer Douglas Peterson.

Sharma, 55, will leave at the end of the year to “pursue other opportunities,” S&P's parent McGraw-Hill Cos. said in an e-mailed statement. Peterson, 53, will take over Sept. 12 and Sharma will work on the company's strategic review in the meantime.

S&P's Aug. 5 decision to reduce the U.S. credit rating to AA+ roiled global markets and boosted demand for Treasuries, sending the yield on the 10-year note, the benchmark for home mortgages and car loans, to a record low 2.03 percent. The New York-based company, which was blamed in an April Senate report for helping fuel the credit crisis, was criticized by the world's most successful investor, Warren Buffett, who said the U.S. should be “quadruple-A.” The cut conflicted with Moody's Investors Service and Fitch Ratings, which kept their AAA grades.