Ayatollah Ali Sistani (Iraq)

Why? Sistani holds Iraq’s Shia community together, despite numerous internal divisions and repeated provocations from Sunni jihadists. Several of his aides have been assassinated, and he remains a target for those who oppose his pragmatic stance or hope to ignite civil war.

Who? He sits atop the insurgency’s hit list. Abu Musab al-Zarqawi and other Sunni militants know Sistani’s death could plunge Iraq into the all-out civil war they want. Rival Shia factions, some implicated in the killing of Sistani’s aides, may also try to kill him.

How? A truck bomb or suicide bomber.

Then what? Sistani is irreplaceable. His status is derived from his education and prestige. No cleric in Iraq enjoys his stature, thanks in part to Saddam’s decimation of much of the clerical elite.

Worst case: Full-scale civil war, both between Sunnis and Shiites, and within the Shia community. Conspiracy theories that the United States killed Sistani become received wisdom, and even reasonable voices blame the United States for allowing it to happen.