Ayatollah Ali Khamenei has spent almost four decades as Shi'ite Iran's supreme leader building a regional power to rival the Sunni states across the Gulf and implacably hostile to the U.S. and Israel - while crushing repeated unrest at home.

As tensions escalate between Iran and Israel, the potential successors to Supreme Leader Ali Khamenei emerge. Discover who the top three candidates are and the implications of a leadership change in Iran.