The group's current No. 2 is believed to be Ayad Abdul-Rahman al-Obeidi, also known as Abu Saleh Haifa, a former Iraqi army officer under Saddam Hussein. But according to Hisham al-Hashimi, an Iraqi expert on IS who advises the Iraqi government, he is not likely to succeed al-Baghdadi as "caliph," since that title is reserved for members of the Prophet Muhammed's Quraish tribe, according to some Muslim scholars. Al-Obeidi is not a member.