Fabien Clain, identified as the voice in an audio recording claiming responsibility for the Paris attacks, is a seasoned jihadist who cut his teeth in the southern French city of Toulouse.
Speaking for the Islamic State group, Clain's chilling propaganda audio warns that the rampage that left 129 dead on Friday was just "the beginning of the storm".
Thought by security sources to be 37 years old, Clain is not a so-called "Facebook jihadi" with cursory religious indoctrination, but someone with sufficient stature to be a mentor among the some 850 French and Belgian militants in Syria.
A convert to Islam in the 1990s, Clain is thought to have been radicalised in the early 2000s.
At the time he and his brother Jean-Michel were active in radical Islamist networks in the Toulouse area, in the thrall of a Frenchman of Syrian origin, Olivier Corel, dubbed the "white imam" and now in his 70s.
They were close to Mohamed Merah, who shot dead seven people, including three Jewish children, in Toulouse in 2012.
Fabien Clain, who goes by the alias Brother Omar, was convicted in 2009 of recruiting jihadists and sentenced to five years in prison, after which he left for Syria.
Clain was considered one of the organisers of a network sending Islamist recruits to fight US soldiers in Iraq.
In April this year Le Monde daily revealed that Clain was suspected of instigating a foiled attack on a church in a southern Paris suburb.
The attack was thwarted when the assailant, Algerian student Sid Ahmed Ghlam, accidentally shot himself in the leg.
After Friday's killing spree in Paris by gunmen and suicide bombers targeting a concert hall, bars, restaurants and the national stadium left at least 129 dead, the Islamic State group audio claimed responsibility.
In the audio, Clain's triumphant voice says "eight brothers wearing explosive belts and carrying assault rifles" conducted a "blessed attack on... Crusader France."
Seven jihadists blew themselves up or were killed by security forces, while an international arrest warrant has been issued for a suspected eighth attacker, named as Salah Abdeslam.
The propaganda statement also made reference to French air strikes on IS positions in Syria.
It said France was guilty of "striking Muslims in the caliphate with their aircraft" and threatened further attacks "as long as it continues its Crusader campaign".