He may be young, but this ambitious London School of Economics grad has worked everywhere: in the Clinton White House, on Howard Dean's presidential campaign, and on U.S. Senate bids on behalf of Barack Obama and Alexi Giannoulias. No wonder Mayor Emanuel promoted Spielfogel to senior adviser in January, an acknowledgment of the degree to which he relies on the policy guru's counsel. "The mayor doesn't make a move without David," says the City Hall insider. Spielfogel lurks in the background of practically every important meeting on the fifth floor. Another measure of his clout: He isn't afraid to disagree with his boss.

Photograph: BROOKE COLLINS/CITY OF CHICAGO