Abu Deraa, a suspected mass killer of Sunnis in 2006, has returned to Iraq amid the push by the Islamic State of Iraq and Syria (ISIS).

Al-Arabiya News reported on the return of Abu Deraa, real name Ismail Hafez al-Lami, to Iraq in the wake of Sunni militants gaining control of Mosul and Tikrit as well as vowing to march on Baghdad. Abu Deraa’s nom du guerre means “Father of the Shield” and his method of killing Sunni militants and civilians during the Iraq War landed him at the top of the American most wanted list, the Telegraph reported in 2006.

Abu Musab al-Zarqawi was killed in 2006 by a U.S. airstrike but claimed responsibility for several suicide bombings, beheadings, executions and other attacks against Shiites during the Iraq War. Following Zarqawi's death, Abu Deraa became notorious for his method of using a drill through the skull to kill Sunnis and his militia forces were believed to be behind the kidnapping and killing of Saddam Hussein's lawyer, Khamis al-Obeidi, in 2007, al-Arabiya News reported.

Little is known about Abu Deraa but it is believed he was a refugee who headed to Sadr City in Baghdad following the destruction of Shiite villages in the southern marshes of Iraq and is married with two children, Jamestown Foundation reported. Abu Deraa started out committing small crimes but rose to power and began killing Sunnis to avenge the deaths of Shiites, al-Arabiya News reported. According to a 2007 report from the Sunday Times, Abu Deraa would give some victims a choice of how they would die and would dump the bodies at what became known as the "Happiness Hotel."

Although reports of his death surfaced in 2007, it is believed he fled to Iran where he has lived for the last few years.