Since Israel began its concerted attack on Iran on Friday, calls for regime change in Iran have grown louder – from hawks in the US Congress to Israeli officials and some Iranian activists abroad.

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.