John Brennan is set to lead the CIA after the fall of David Petraeus. He is a CIA veteran who has spent the last four years evolving the White House counter-terrorism strategy.
Brennan missed the top spot in 2009 over his support to using some "enhanced interrogation techniques" under the Bush administration. His appointment as deputy national security adviser for homeland security and counter-terrorism in 2009 did not require a Senate confirmation and thus evaded congressional scrutiny.
A trained spy, Brennan rose quickly to become a counter-terrorism analyst and manager in the agency's intelligence directorate. Later, he served as interim director of the National Counter-Terrorism Center during 2004 -2005.