Who is Muqtada al-Sadr?
(CNN) -- How has Muqtada al-Sadr gotten so much attention? Believed to be about 30 years old, al-Sadr is the son of a grand ayatollah but U.S. officials think his support is relatively small, and concentrated among the young and poor.
Still, al-Sadr's followers have battled coalition troops in Baghdad and Tuesday took control of the holy city of Najaf, a coalition source said. Al-Sadr's followers control the governor's office, police stations and the Imam Ali mosque, one of Shia Muslim's holiest shrines.
U.S. officials worry that if al-Sadr's movement grows in popularity, "then we would have a challenge on our hands," said U.S. Army Maj. Gen. Martin Dempsey.
The following is a brief explanation of how al-Sadr fits into the framework of Shia Islam.
Shia Muslims recognize four grand ayatollahs, the senior-most of spiritual leaders, that comprise the main Shia "seminary" in the holy city of Najaf.
The grand ayatollahs are Ali al-Sistani, Muhammad Sayid al-Hakim, Muhammad Ishaq Fayadh and Bashir Hussein al-Najafi.
Fayadh and Najafi almost exclusively focus on spiritual matters. Fayadh, an Afghan, is considered the senior-most leader by Afghan Shias. South Asian Shiites look to Najafi, who is of Pakistani origin.
Hakim, an Iraqi, is the uncle of Ayatollah Muhammad Baqir al-Hakim, the former head of the Supreme Council for the Islamic Revolution in Iraq. He was killed in a car bomb outside the Imam Ali mosque in August 2003. Hakim and Grand Ayatollah Mohammed Baqir al-Sadr founded a political Islamic movement in the late 1950s.
Baqir al-Sadr was executed by Saddam Hussein's regime in 1980, and his cousin, Grand Ayatollah Mohammed Sadiq al-Sadr, was assassinated in 1999. Two of the grand ayatollah's sons were killed with him..
The remaining son, Muqtada al-Sadr, did not finish training at the Hawzah and has no formal Islamic standing. He takes his spiritual direction from an ultra-conservative, Iran-based, Iraqi-exiled cleric, Ayatollah Kazim al-Haeri, who was a student of Bakir al-Sadr.
Al-Sistani, who is the Shia spiritual leader in Iraq, was a student of Grand Ayatollah Abu Gharib al-Qassim al-Khoei, whose son, Ayatollah Abdul Majid al-Khoei, was killed outside the Imam Ali mosque by a mob of Muqtada al-Sadr's supporters in April 2003. Al-Sistani is an Iranian by birth, but spent most of his life in Iraq.
An Iraqi judge has issued 25 arrest warrants in connection with Khoei's death -- including one for al-Sadr's arrest.