Donald Trump says US forces killed Abu Bakr al-Baghdadi in a "daring and dangerous" early morning raid by US Special Forces on Sunday.
Speaking from the White House, President Donald Trump said Abu Bakr al-Baghdadi detonated his suicide vest after fleeing into a tunnel in northwest Syria, chased by US military dogs.
The fugitive leader of the Islamic State (IS) group came to prominence in 2014, when he announced the creation of a "caliphate" in areas of Iraq and Syria.
IS carried out multiple atrocities that resulted in thousands of deaths.
The jihadist group imposed a brutal rule on almost eight million people and was behind many attacks around the world. The US declared the "caliphate" defeated earlier this year although IS militants remain active in the region and elsewhere.
The killing of Baghdadi is a major victory for Mr Trump, who has been heavily criticised for his decision to pull US troops out of northern Syria earlier this month and is fighting an impeachment inquiry launched by Democrats.
In an unusual Sunday morning statement, Mr Trump said Baghdadi died after running into a dead-end tunnel in Idlib province, "whimpering, crying and screaming all the way", as he was chased by military dogs.
Baghdadi was accompanied by three of his young children, Mr Trump said, and detonated his suicide vest, killing them all. The blast mutilated Baghdadi's body but an on-site DNA test confirmed his identity.
"The thug who tried so hard to intimidate others spent his last moments in utter fear, in total panic and dread, terrified of the American forces bearing down on him," Mr Trump said.
Eleven children were removed, uninjured, and taken into care by a third party whom the president declined to name. US soldiers captured and later imprisoned several Islamic State fighters.
What is known about the operation?
The location near the Turkish border was far from where Baghdadi had been thought to be hiding along the Syria-Iraq border. Many parts of Idlib are under the control of jihadists opposed to IS but rival groups are suspected of sheltering IS members.
Baghdadi had been under surveillance for "a couple of weeks" and "two or three" raids had been cancelled because of his movements, Mr Trump said, describing the IS leader's move to Idlib as part of a plan to rebuild IS.
'Caliphate' defeated but IS remains a threat
The forces targeted the compound using eight helicopters, which were met with hostile fire, Mr Trump said. The commandos entered the building by blowing holes in the wall, avoiding the main door which was booby-trapped.
When Baghdadi detonated his vest, the president said, the tunnel caved on him. One of the US dogs was injured in the operation.
"He was a sick and depraved man, and now he's gone," Mr Trump said. "He died like a dog, he died like a coward."
No US soldiers were killed but a number of Baghdadi's followers also died while others were captured, the president said. The special forces spent two hours in the area, and gathered "highly sensitive material".
Syrian Kurdish-led forces - one of the main US allies in northern Syria until Mr Trump withdrew US troops from the area this month - said they had carried out a "historic" joint operation.
Mr Trump praised them, as well as Russia - which opened up the airspace it controls for the operation - Iraq, Turkey and Syria for giving "certain support" to the operation.
'World's most wanted man'
Baghdadi, whose real name was Ibrahim Awwad Ibrahim al-Badri, had a reputation as a highly organised and ruthless battlefield tactician. He was described as the world's most wanted man.
He was born near Samarra, north of Baghdad, in 1971, and reports suggest he was a cleric in a mosque in the city around the time of the US-led invasion in 2003.
Some believe he was already a jihadist during the rule of former Iraqi leader Saddam Hussein. Others suggest he was radicalised during the time he was held at Camp Bucca, a US facility in southern Iraq where many al-Qaeda commanders were detained.
Baghdadi emerged in 2010 as the leader of an umbrella group that included al-Qaeda in Iraq, and rose to prominence when IS militants captured the Iraqi city of Mosul in 2014, when he declared the creation of a "caliphate".
That was the only time Baghdadi was seen in public. He reappeared in a video released by IS earlier this year.
In October 2011, the US officially designated him a "terrorist" and offered a reward of $US10million for information leading to his capture or death. This was increased to $25m in 2017.
American forces have tried for years to track down the head of the Islamic State.