New world news from Time: Abu Bakr al-Baghdadi Is Dead. Here’s What to Know About the Deceased Islamic State Leader

On Sunday morning, President Donald Trump announced the death of a man he described as the “world’s number-one terrorist leader:” Abu Bakr al-Baghdadi, the head of the Islamic State.

Here’s what to know about the reportedly deceased leader of the infamous terrorist group:

Early life and radicalization

Al-Baghdadi’s was born in 1971 in the city of Samarra, Iraq, northwest of Baghdad as Ibrahim bin ‘Awad bin Ibrahim al-Badri ar-Radawi al-Husseini as-Samara’i. His family were Sunni Muslim members of tribe that claims to be descended from the Prophet Muhammad. Al-Baghdadi is thought to have shown signs of radicalization years ago, joining an extreme branch of the Sunni dissident group the Muslim Brotherhood as a youth.

His formation into the future leader of ISIS is believed to have taken place after he was captured by U.S. forces in Iraq while visiting a friend in Fallujah. While imprisoned Camp Bucca, a notorious facility known for generating Sunni jihadists, he developed connections with future ISIS fighters, including Abu Mohammad al-Adnani, who later became ISIS’s spy chief.

Al-Baghdadi’s rise, both in prison and later, is thought to have been driven by his ideological and religious leadership. He earned a PhD in Islamic Studies, and was known for his dogmatic approach to Islam.

al-Qaeda in Iraq to ISIS

After leaving prison, al-Baghdadi rose in the ranks of the Iraqi group affiliated with al-Qaeda, known as al-Qaeda in Iraq. The group had been founded by a Jordanian national, Abu Musab al-Zarqawi, who had pledged allegiance to Osama bin Laden after the U.S. invasion of Iraq in 2005. Over time, the group gained a violent reputation, carrying out suicide bombings; fighting U.S. and Iraqi government troops; and enforcing a strict interpretation of Sharia law, which included beheadings.

When al-Zarqawi was killed by U.S. force in 2006, several leaders took turns at al-Qaeda in Iraq helm. But the organization began to shift more rapidly after al-Baghdadi took over in 2010. In 2011, he cut the organization’s connection to al-Qaeda and renamed the group Islamic State in Iraq. The group also introduced a new ambition: creating single Sunni regime that ruled over the entire Arab world. Two years later, the organization was renamed again to reflect the greater scale of its ambitions – Islamic State of Iraq and Greater Syria, or ISIS.

Under al-Baghdadi’s leadership, the Islamic State took over territory in Syria and Iraq. The group worked to establish its authority over these area, enforcing Sharia law, collecting taxes in Mosul, Iraq; capturing oil fields and refineries in Syria; and setting up a government of Raqqa, Syria, which included courts, a school and a bus service.

Al-Baghdadi also promoted the idea that while Muslims must follow Allah, non-Muslims are the slaves of Muslims. After al-Baghdadi’s wife was captured, she informed her interrogators that women and girls had had been used as sex slaves for ISIS militants, and that Kayla Mueller, an American aid worker, was raped and tortured by al-Baghdadi himself before her death.

Terrorists who claimed to be affiliated with the Islamic State — or who ISIS claimed as their affiliates— took responsibility for terrorist attacks abroad. These include the downing of a Russian jet in 2015 and a series of terrorist attacks in France.

Today, a military coalition led by the United States has wrested control of cities and territory formerly controlled by ISIS, and thousands of ISIS fighters are being held in Kurdish-led Syrian Democratic Forces detention centers. However, there are concerns that the withdrawal will give these fighters an opportunity to escape — and give ISIS a chance to rebuild.

What does his death mean?

Al-Baghdadi’s death is a crucial symbolic victory in the battle against the embattled terrorist group, because ISIS held that he was the head of a worldwide caliphate, a single Sunni regime which intended to rule over the entire Arab world. This ideology led the group to take over significant swaths of territory, at one point controlling territory in Iraq and Syria that was equivalent to the size of Great Britain. It also built an international terrorist brand that drew recruits from the Middle East, Europe and North America, inspiring terrorist attacks as far away as San Bernardino, Calif.

The death of al-Baghdadi is also a victory for the Trump administration, which has faced criticism from both sides of the political field over the last month for the decision to withdraw U.S. troops from Syria. Critics say that while the Islamic State is weak, the withdrawal of American troops may give Islamic State militants an opportunity to recover. President Trump has repeatedly asserted that the Islamic State has been defeated, and that the military presence of other countries, including Turkey, will be enough to keep the terrorist group at bay.

Trump declared that the capture or killing of al-Baghdadi had been the “top national security priority of his Administration.” U.S forces had searched for al-Baghdadi for more than five years. Al-Baghdadi developed a reputation for maintaining elaborate efforts to keep secrecy, avoiding cellphones and keeping face concealed from all but a chosen few. Trump said that plans to capture al-Baghdadi had been delayed because the terrorist leader frequently changed his travel plans.