Khan was the dominant ideologue of the bombers and is believed to have recruited the others to carry out the attacks.
Khan had travelled to Taliban-controlled Afghanistan in the late 1990s in the company of a man called Imran. He regularly visited Pakistan with Shahzad Tanweer and they are believed to have trained in Islamist camps.
Growing up in the Beeston and Holbeck area of Leeds, Khan is remembered as a studious boy who seldom got into trouble., but he was also timid and subject to bullying.
During his teenage years Khan drank, and, he told friends, experimented with drugs. A fight in a nightclub appears to have been the catalyst in turning him towards religion.
Initially he attended mainstream mosques while living a seemingly normal life with his wife, Hasina, and their young daughter in Dewsbury.
He worked for the Benefits Agency and then as an administrative assistant for the Department of Trade and Industry, where, fluent in Urdu and Punjabi, he helped to promote British firms overseas.
Later, he worked as a classroom "mentor" at Hillside primary school, where he was regarded as "having a real empathy with difficult children" who saw him as a "role model".
At this time he visited the Houses of Parliament with his local MP, Jon Trickett, where he met Hilary Benn, the International Development Secretary.
In 2003 Khan began mixing with radical Muslims and espousing a virulent form of fundamentalist Islam. He gave talks in a room below a mosque in Beeston, which was used as a youth club and gym.
One of the gyms in the area was known as the "al-Qa'ida gym" because of those who frequented it, while a local bookshop was used to watch extremist material. Khan used the opportunities such places presented to identify candidates for indoctrination, according to the report.
Khan, Shahzad Tanweer and Hasib Mir Hussain were banned at one time from mosques in Leeds.
Just weeks before the bombing, Khan went white-water rafting with Tanweer on a "team bonding" exercise.
Khan and Tanweer, who had become close, also went to Islamist events outside the Leeds area and are believed to have held talks with others of a similar mindset in the North and the Midlands and spent hours accessing websites preaching a militant fundamentalist message. There is little evidence, however, that Khan was using the internet at home an attempt, it is believed, to ensure that his wife knew little about his illicit activities.
Two months after the bombings Khan appeared on a video praising the al-Qa'ida leader Osama bin Laden and his deputy Ayman al-Zawahri. He declared: "We are at war and I am a soldier."
Shahzad Tanweer
Tanweer was Mohammad Sidique Khan's lieutenant in the bomb plot, accompanying him to Pakistan to seek meetings with al-Qa'ida.
He is said to have taken Islam seriously from an early age but did not show any sign of following a militant path.
Tanweer's father was a prominent local businessman and he had a comfortable lifestyle before studying at Leeds Metropolitan University.
Tanweer was a gifted sportsman particularly at cricket and athletics and loved martial arts.
Tanweer, known by the nickname "kaka", or little one, liked to show off a flamboyant lifestyle and drove a red Mercedes. He was also known to spend time and money on clothes and grooming. But the Western trappings masked a growing radicalism.
He travelled to Pakistan at the end of 2004, where he is said to have attended a madrassa, or religious school, in Lahore. It has also been claimed that just a few months before the bombings, Tanweer met a leader of the outlawed radical group Jaish-e-Muhammad, which is said to have links to al-Qa'ida.
Tanweer worked for a few hours a week as an assistant in the fish and chip shop run by his father. Despite this he left an estate valued at £121,000 after taxes and debts. It is not known where the money came from.
Jermaine Lindsay
Lindsay has been described as the outsider of the group. He was of Jamaican, rather than Pakistani descent, and had no connection with the Beeston area of Leeds.
Lindsay, however, was responsible for the greatest loss of life on 7 July when he blew himself up on a Piccadilly Line train close to Kings Cross station, killing 26 people.
Lindsay's stepfather is said to have been harsh towards him while he was growing up. His mother converted to Islam in 2000. He converted almost immediately afterwards and took the name Jamal.
In 2002 his mother moved to the US to live with another man, leaving him alone at the family home in Huddersfield. This is said to have been a deeply traumatic experience. Lindsay married a white British convert to Islam, Samantha Lewthwaite, who he had met through the internet and at a "Stop the War" march. They lived initially in Huddersfield before moving to Aylesbury, Buckinghamshire.
Mrs Lindsay said her husband's behaviour had become increasingly erratic in the days prior to the bombings, to the point that she ordered him out of the house hours ahead of the attacks.
Lindsay is said in the reports to have been strongly influenced by the extremist preacher Abdallah al Faisal, who was also of Jamaican origin and who is serving a prison sentence for incitement to murder and racial hatred.
Following a review of intelligence MI5 discovered they had Lindsay's telephone number. They obtained it while tracking telephone calls made by Mohammad Sidique Khan in 2004 during surveillance of a group of Islamists who were subsequently arrested for another alleged plot.
Hasib Hussain
Hussain was the youngest of the suicide bombers. The blast he carried out took place an hour after the others and on a bus rather than a train.
It had been assumed that 18-year-old Hussain had lost his nerve or that he'd been confused by delays on the Northern Line tube. However it emerged yesterday that Hussein had stopped off and bought batteries from a high-street shop for his bomb for a second attempt after failing the first time.
He could not get back into the underground system because of the security alert following the earlier bombings, and blew up the bus instead. Born on 16 September 1986, he had a normal upbringing in the Holbeck area of Leeds.
Always big for his age and "chubby-faced", Hasib Hussain lived at the family home all his life, going to local schools. His family said he was hoping to go to university, but he was not a high academic achiever.
But he appeared to have changed after his parents sent him to Pakistan following concerns about him "going a bit wild".
As he became more and more serious about his religion, he lost five stone and would spend hours studying texts, the report said.
Hussain's religious convictions became even more vociferous following a pilgrimage to Saudi Arabia in 2002 with his family. He was vocal about his support for al-Qa'ida in school and regarded the 9/11 hijackers as martyrs.
His father, a retired foundry worker, said another of the bombers, Khan, would come to their home in Colenso Mount and talk with Hasib and his elder brother, Imran, for hours, along with a third bomber, Tanweer.
Mr Hussain also described how he and his wife waved their son off on his trip to London, oblivious of his intentions.
It was Hasib Hussain's mother who reported him missing on the evening of 7 July, still unaware of what he had done, providing police with their first big breakthrough in their investigation.
