Kata’ib Hezbollah is one of the Popular Mobilization Units (PMU) that were recruited to fight the Islamic State after the Iraqi armed forces collapsed and Mosul, Iraq’s second-largest city, fell to IS in June 2014. The first six PMUs were formed by five Shiite militias that all received support from Iran, plus Muqtada al-Sadr’s Iraqi nationalist Peace Company, the reincarnation of his anti-occupation Mahdi Army militia, which he had previously disarmed in 2008 under an agreement with the Iraqi government.
Kata’ib Hezbollah was one of those five original Shiite militias and it existed long before the fight against IS. It was a small Shiite group founded before the U.S. invasion of Iraq in 2003, and was part of the Iraqi Resistance throughout the U.S. occupation. In 2011, it reportedly had 1,000 fighters, who were paid $300 to $500 per month, probably mainly funded by Iran. It fought fiercely until the last U.S. occupation forces were withdrawn in December 2011, and claimed responsibility for a rocket attack that killed 5 U.S. soldiers in Baghdad in June 2011. Since forming a PMU in 2014, its leader, Abu Mahdi al-Muhandis, has been the overall military commander of the PMUs, reporting directly to the National Security Adviser in the Prime Minister’s office.