As chief of staff to Health and Human Services Secretary Kathleen Sebelius, Petrou works behind the scenes to keep the secretary’s office running and advance Sebelius' agenda. That means overseeing a $70 billion department, while at the same time trying to steer historic health-care reform legislation through Congress. Petrou is known for her excellent management skills and her vast connections on Capitol Hill. Though she’s not a health- policy expert, she had plenty of exposure to the issue during nearly two decades working for former Senate Majority Leader Tom Daschle (D-S.D.). Petrou is one of a handful of top Daschle lieutenants still well-positioned in the Obama administration, despite Daschle having to drop his nomination for HHS secretary because of unpaid taxes.