Anwar al-Awlaki, a radical American Muslim cleric of Yemeni descent, was linked to a series of attacks and plots across the world - from 11 September 2001 to the shootings at Fort Hood in November 2009.
After surviving several attempts on his life, he was killed in a US drone strike in western Yemen on 30 September 2011.
In recent years, Awlaki's overt endorsement of violence as a religious duty in his sermons and on the internet is believed to have inspired new recruits to Islamist militancy.
Following the failed attack, US President Barack Obama took the extraordinary step of authorising the Central Intelligence Agency to kill him. Soon afterwards, Awlaki survived an air strike on a suspected al-Qaeda base in southern Yemen.
His family said he was not a terrorist and launched a legal challenge to stop the US executing one of its citizens without any judicial process.
Awlaki was born in 1971 in the southern US state of New Mexico, where his father, Nasser, a future Yemeni agriculture minister and university president, was studying agricultural economics.
He lived in the US until the age of seven, when his family returned to Yemen.
After studying Islam during his teenage years, Awlaki returned to the US to gain a degree in civil engineering from Colorado State University and a master's in education at San Diego State.
In 1994, he married a cousin from Yemen and took a part-time job as imam at the Denver Islamic Society.
Awlaki later became imam at a mosque in Fort Collins, Colorado, before returning to San Diego in 1996, where he took charge of the city's Masjid Ar-Ribat al-Islami mosque.
During his four years there, his sermons were attended by two future 9/11 hijackers, Khalid al-Midhar and Nawaf al-Hazmi. The two men were also seen attending long meetings with the cleric.
In early 2001, he moved to the Dar al-Hijrah mosque in Falls Church, Virginia, which was attended by Hazmi and a third hijacker, Hani Hanjour.
The 9/11 Commission found the connections to be suspicious, though FBI agents who interviewed him said they doubted he knew of the plot.
It also emerged that in 1998 and 1999, while serving as vice-president of an Islamic charity that the FBI described as "a front organisation to funnel money to terrorists", Awlaki was visited by Ziyad Khaleel, an al-Qaeda operative, and an associate of Sheikh Omar Abdel Rahman, who was serving a life sentence for plotting to blow up landmarks in New York.
In 2002, he left the US for the UK, where he spent several months giving a series of popular lectures to Muslim youths.
Unable to support himself, Awlaki returned to Yemen in early 2004, and moved to his ancestral village in the southern province of Shabwa with his wife and children.
He soon became a lecturer at al-Iman University, a Sunni religious school in Sanaa headed by Abdul-Majid al-Zindani, a cleric who has been designated a terrorist by both the US and UN for his suspected links with al-Qaeda.
In 2004, Zindani was listed as a "specially designated global terrorist" by the US Treasury Department and the UN, but Yemen took no steps to freeze his assets.
Former students include John Walker Lindh, known as the "American Taliban", and several suspected militants.
In August 2006, Awlaki was detained by the Yemeni authorities, reportedly on charges relating to a plot to kidnap a US military attache.
He said he was interviewed by FBI agents during his subsequent 18 months in prison, and believed the US had asked the Yemeni authorities to prolong his detention.
Following his release, Awlaki's message seemed overtly supportive of violence, railing against the US-led invasions of Afghanistan and Iraq, and the killing of Muslims in covert operations in Pakistan and Yemen.
He incited violence in a number of texts via his website, his Facebook page and many booklets and CDs, including one called "44 Ways to Support Jihad".
Such materials have been found in the possession of several convicted English-speaking militants in Canada, the UK and US.
In July 2009, the cleric stated in a blog post that a Muslim soldier who fought other Muslims was a "heartless beast, bent on evil, who sells his religion for a few dollars". Following the shootings, Awlaki called Maj Hasan a hero.
"My support to the operation was because the operation brother Nidal carried out was a courageous one," he told al-Jazeera.
Awlaki again hit the headlines in January, when US officials said he might have met Umar Farouk Abdulmutallab at al-Iman University, while the latter was studying Arabic there in November or December 2009.
The 23-year-old was at the same time receiving his final training and indoctrination from members of al-Qaeda in the Arabian Peninsula, ahead of his alleged suicide mission, they said.
Awlaki later acknowledged that he had "communications" with the Nigerian in late 2009, but denied any role in the alleged attack.
In May 2010, Faisal Shahzad, the US citizen of Pakistani origin who has admitted attempting to bomb New York's Times Square, said he had been inspired by the violent rhetoric of Awlaki, according to US officials.
Two months later, the US treasury department named Awlaki a "specially designated global terrorist", blocked his assets and made it a crime for Americans to do business with him or for his benefit.
And in late October of that year, he was the only man named by the head of the UK's Secret Intelligence Service (SIS) when he outlined major threats to the country in his first public speech.
Only days later, two suspect packages containing bombs and addressed to synagogues in the US city of Chicago were sent from Yemen. They were carried by plane and intercepted in the UK and Dubai.
US officials blamed al-Qaeda in the Arabian Peninsula for the failed attack and again linked the plot to Awlaki.
In late 2010, the Yemeni authorities surprised many by putting him on trial in absentia, charged with inciting violence against foreigners in connection with the killing of a French security guard at an oil company's compound.
According to prosecutors, Awlaki and his cousin, Osman, were in contact with the alleged attacker, Hisham Assem. Yemeni officials had until then said they had no legal justification to detain Awlaki.
At the time, he was thought to be hiding in the mountainous governorates of Shabwa and Marib, under the protection of the large and powerful Awalik tribe, to which he belongs.