Mohammad Sidique Khan, a 30-year-old married father-of-one, was the oldest of the four suicide bombers who attacked London's transport network, and is thought to have taken the lead role in the plot.
The naming of Mohammad Sidique Khan as the suspected ringleader of the four men behind London's day of terror stunned many of those who had known him.
Colleagues struggled to reconcile their memories of the dedicated classroom assistant with the knowledge that he had detonated enough explosives on a Circle Line underground train near Edgware Road to kill himself and six others.
The classroom assistant was respected by teachers and parents
Born in Leeds on 20 October 1974, Khan was - in common with two of the other three 7 July bombers - the son of Pakistani immigrants who had taken British citizenship.
The youngest of six children, he grew up in Beeston, a deprived, ethnically mixed area of the city. Educated locally, he is remembered as a quiet, studious boy who was never in trouble but was sometimes bullied.
Friends from his teenage years recall a highly Westernised young man who insisted on being called "Sid".
After school, he worked in low-level government clerical jobs before leaving to study for a degree in business studies at Leeds Metropolitan University.
Here he met his future wife, Hasina, a British Muslim of Indian origin. Despite initial disapproval from their families, they married on 2 October 2001 and had a daughter in May 2004.
While still at university, his interest in helping disadvantaged young people appears to have developed, and he took on part-time youth and community work before graduating with a second-class degree in business studies in 1996.
After his marriage in 2001, Khan moved out of Beeston to nearby Batley, and then to Dewsbury, but remained a part of the local community through his work as a primary school teaching assistant and youth worker.
His role at the school was that of "learning mentor", working with children who were struggling with their work, as well as those with behavioural problems.
He was highly regarded by both teachers and parents, showing a real talent for encouraging difficult children, many of whom viewed him as a role model.
MOHAMMAD SIDIQUE KHAN
Oct 1974: Born in Leeds
Late 1990s: Starts youth work
2001: Begins work as learning mentor
Oct 2001: Marries
Early 2003: Makes Hajj visit to Mecca with wife
Apr 2003: Camping trip with fellow bomber Shehzad Tanweer and other young men
July 2003:Attends Pakistan training camp
Feb - Mar 2004:Comes onto MI5 radar amid surveillance of separate bomb plot
May 2004: Daughter born
June 2004:MI5 focus on more dangerous and urgent suspects
Sep-Nov 2004: Long absence from work, job ends
Nov 2004-Feb 2005: Visits Pakistan with Tanweer
June 2005: Recce visit to London
7 July 2005:Bombs Tube train near Edgware Road, killing six
Sep 2005:'Video will' filmed in English released to an Arabic news channel
By the time he began this job in 2001, he was clearly serious about his Islamic faith. He prayed regularly at school and attended the local mosque on Fridays.
He told associates that he had turned to religion after a far from blameless youth that had seen him involved in fights, as well as bouts of drinking and drug-taking.
Colleagues said there was no suggestion of extremism in the way he talked about his religion - in fact, he had spoken out against the 11 September attacks on the US at school.
But some now recall a subtle change in his character after he had been in the job for about a year. He is said to have become more introverted, and on a couple of occasions displayed an intolerant attitude at odds with his normal easy-going manner.
Throughout his time at the school, Khan's social life revolved around the mosques and Islamic groups of Leeds, Huddersfield and Dewsbury - and included some voluntary work with Muslim youths, arranging activities such as camping and white-water rafting.
In common with his work at the school, Khan became identified as someone whom young people looked up to.
It is possible that he used this as an opportunity to identify candidates for recruitment to the radical brand of Islam he was now espousing. He and two of the other 7 July bombers, 22-year-old Shehzad Tanweer and 18-year-old Hasib Hussain, were observed spending a lot of time together in the months before the bombings.
Khan's once-promising career in education ended with his dismissal in late 2004 after a period of increasingly poor attendance at work that culminated with a period of sick leave stretching from 20 September to 19 November.
He then travelled to Pakistan, accompanied by Tanweer. It is unclear if the pair received any particular training while here, but they are thought to have had some contact with members of Osama Bin Laden's al-Qaeda network.
After the 7 July attacks, MI5 said it had come across Khan and Tanweer "on the periphery" of another operation, the Parliamentary Intelligence and Security Committee reported.
That operation - and fuller details of what the security services knew - has now been revealed. Khan is now known to have been monitored on four separate occasions in February and March 2004 because he was an associate of a group of men plotting to build a massive fertiliser bomb.
Khan got to know the men through mutual sympathisers in a broad but loose jihadi international network spanning North America, the UK and Pakistan.
In evidence that emerged during the 2006-07 trial of the seven men accused of planning a fertiliser bomb plot, the Old Bailey heard that Khan had been to the same terrorism training camp as other members of that conspiracy and maintained links on his return.
What MI5 then knew of Khan's intent remains unclear. In the report to MPs, and subsequent briefings to the media, security sources have stressed that Khan and Tanweer, who also came onto the radar, were not considered "essential" because there was no intelligence they were actually planning a terrorist attack.
At worst, Khan was thought to be involved in fraud and, according to the MPs' report, he had not been identified, only watched. With mounting workload, including the uncovering of a separate major plot in the middle of 2004, anti-terrorism officers focused on other suspects.
Khan was also the subject of reporting to the security services from "detainees" outside the UK, but his true identity was not revealed until after the 7 July attacks.
Failures to show a photograph of Khan to these detainees before the attacks was a "missed opportunity", the report said.
One of these detainees was Mohammed Junaid Babar, a jihadi sympathiser who became a key prosecution witness in the fertiliser bomb plot trial. Babar attended the same 2003 training camp as Khan and recognised his photograph on television after the London bombings.
In June 2006 computer expert Martin Gilbertson claimed he had warned West Yorkshire police about the extremist views of Khan and Tanweer when he worked at an Islamic bookshop in Beeston. The police later said they had no record of any letter from him.
Two months after the deaths of the four bombers and their 52 victims, a video statement recorded by Khan before the attacks surfaced.
In an unmistakeably Yorkshire accent, he defended the impending suicide attacks, declaring himself "a soldier" fighting a war against Western governments and their supporters in the general population.