BEIRUT - Before he became head of an al-Qaida-linked group that is one of the most feared bands of radicals fighting the Syrian regime, he was a teacher of classical Arabic who fought American troops in Iraq and quickly rose through the ranks of the global terrorist network.
Little else is known about Abu Mohammad al-Golani, the man who leads the Nusra Front - including where he is now or even if he is still alive.
"His identity is really a bit of a mystery," said Charles Lister, analyst at IHS Jane's Terrorism and Insurgency Center.
Syrian state media said last week that al-Golani, also known as the emir of Jabhat al-Nusra, was killed in fighting in a coastal stronghold of Syrian President Bashar Assad's government. But rebels deny that, describing the report as propaganda.
Al-Golani is so mysterious that no one can say with certainty what his real name is. Al-Golani is a nom de guerre, indicating he was born in the Israeli-occupied Golan Heights.
A native of Syria, he joined the insurgency after moving to Iraq, regional intelligence officials say.
There, he advanced through al-Qaida's ranks and eventually returned to Syria shortly after the uprising against Assad began in March 2011.
Lister, who follows Syria's rebel brigades, said he is skeptical about reports of al-Golani's death. If true, they would have stirred up considerable chatter on jihadist forums and social media platforms, he said.
Rebel leaders in Syria agree.
"We haven't seen anything unusual among the ranks of Jabhat al-Nusra fighters that suggest their leader has been killed," Islam Alloush, spokesman for Jaysh al-Islam, or the Islamic Army rebel umbrella group, told The Associated Press via Skype.
Iraqi, Jordanian and Lebanese security officials describe the 39-year-old al-Golani as one of the top leaders of al-Qaida.
According to two senior Iraqi military intelligence officials, he was once a teacher of Arabic before moving to Iraq, where he turned to militancy and eventually became a close associate of Abu Musab al-Zarqawi, the Jordanian-born leader of the militant group al-Qaida in Iraq.
After al-Zarqawi was killed by a U.S. airstrike in 2006, al-Golani left Iraq, briefly staying in Lebanon, where he offered logistical support for the Jund al-Sham militant group, which follows al-Qaida's extremist ideology, the officials said.
He returned to Iraq to continue fighting but was arrested by the U.S. military and held at Camp Bucca, a sprawling prison on Iraq's southern border with Kuwait. At that camp, where the U.S. military held tens of thousands of suspected militants, he taught classical Arabic to other prisoners, according to the officials, who spoke on condition of anonymity because they were revealing information from secret files.
After his release from prison in 2008, al-Golani resumed his militant work, this time alongside Abu Bakr al-Baghdadi, the head of al-Qaida in Iraq - also known as the Islamic State of Iraq. He was soon appointed head of al-Qaida operations in Mosul province.
Shortly after the Syrian uprising began, al-Golani moved into Syrian territory and, fully supported by al-Baghdadi, formed the Nusra Front, which was first announced in January 2012.
A leader of Jordan's ultra-Orthodox and banned Salafi movement said al-Baghdadi sent al-Golani and Abu Jleibeen, a senior al-Qaida operative who has a relationship by marriage to al-Zarqawi, to fight in Syria, where al-Golani was named "general emir" of Nusra and Abu Jlebeeb an emir of the southern Daraa province, birthplace of the Syrian uprising. He spoke on condition of anonymity, fearing police retribution.
Under al-Golani's leadership, Nusra has grown into one of the most powerful rebel groups, with an estimated force of 6,000 to 7,000 fighters across the country.
The U.S. State Department, which placed Nusra on its list of terrorist organizations in December 2012, said the group has claimed nearly 600 attacks, including suicide attacks, small-arms operations and bombings in major cities.
"Through these attacks, al-Nusra has sought to portray itself as part of the legitimate Syrian opposition while it is, in fact, an attempt by al-Qaida in Iraq to hijack the struggles of the Syrian people for its own malign purposes," the department said.
Al-Golani gained prominence in April, when he rejected an attempted takeover of Nusra by al-Baghdadi, revealing a widening rift within al-Qaida's global network. Al-Golani distanced himself from claims that the two groups had merged into a group called the Islamic State of Iraq and the Levant (ISIL), as announced by al-Baghdadi.
Instead, he pledged allegiance directly to al-Qaida's leader, Ayman al-Zawahri, who was said to be against al-Baghdadi's bid to merge both groups, and said his group will continue to use Jabhat al-Nusra as its name.
In a recording, the soft-spoken man vowed that allegiance to al-Zawahri will not change the group's behavior inside Syria.
"We say to our people in Syria that Jabhat al-Nusra will continue to defend your religion, your dignity and blood and will not change its behavior toward you or other fighter groups," he said.
Al-Golani himself was listed by the State Department as a "specially designated global terrorist" in May.
In another recording, he said his ultimate goal is the overthrow of Assad and the institution of Shariah law throughout the country.
Despite some friction with members of the mainstream Free Syrian Army rebel umbrella group, the two sides often work together against Assad's troops in opposition-held areas. The group is more popular in Syria than the ISIL, which is largely made up of foreign fighters and has been criticized for its brutality and for trying to impose a strict version of Islamic law in areas under its control.
Nusra, by contrast, is made up mostly of Syrians, many of whom fought American forces in Iraq.
Rebels acknowledge knowing close to nothing about al-Golani. The Nusra Front, like al-Qaeda in Iraq, obscures the real identity of its senior leaders.
A Jordanian security official said only the top echelon in al-Qaida know al-Golani's real name, but he's commonly known to them as "Al Sheikh Al Fateh," the Conqueror Sheik. The official spoke on condition of anonymity because he was not allowed to make statements to journalists.
An Internet search for al-Golani's picture turns up just one, an image of a young, bearded man in black fatigues.
"It's difficult to know anything," Alloush said. "He doesn't come out in the open."
Abdul-Zahra reported from Baghdad, Iraq. Associated Press writers Jamal Halaby in Amman, Jordan, and Deb Riechman in Washington contributed to this report.