Valerie Jarrett - The Other Power in the West Wing

From The New York Times:

A Chicagoan who helped Mr. Obama navigate his rise through that city’s aggressive politics, Ms. Jarrett came to Washington with no national experience. But her unmatched access to the Obamas has made her a driving force in some of the most significant domestic policy decisions of the president’s first term, her persuasive power only amplified by Mr. Obama’s insular management style.
      

From the first, her official job has been somewhat vague. But nearly four years on, with Mr. Obama poised to accept his party’s renomination this week, her standing is clear, to her many admirers and detractors alike. “She is the single most influential person in the Obama White House,” said one former senior White House official, who like many would speak candidly only on condition of anonymity.