CAIRO - The Muslim Brotherhood's Mohamed Mursi has cast himself as a reluctant latecomer to the race for the Egyptian presidency who is running to serve the nation and God, striking a conservative tone with promises to implement Islamic law. A stocky, bespectacled 60-year old with a grey-white beard, Mursi has travelled across Egypt to lay out his group's "renaissance project" - an 80-page document covering economic, social and foreign policies which the Brotherhood says are forged around its "centrist understanding" of Islam. Presenting himself as the only Islamist in a field where there are two others, Mursi has repeatedly promised to implement Islamic sharia during campaign rallies peppered with references to the Koran, God and the Prophet Mohammad and occasionally interrupted by pauses for mass prayer. But critics say he has seldom spelt out what that promise could mean in practical terms for a country where piety runs deep and the constitution already defines Islamic law as the main source of legislation. The rhetoric emanating from his campaign has alarmed non-Islamists, not least the Christians who make up about a tenth of the country's 82 million people, who are unconvinced by promises that personal freedoms will be safe in a Brotherhood-led Egypt. "It was for the sake of the Islamic sharia that men were ... thrown into prison. Their blood and existence rests on our shoulders now," Mursi said during one campaign rally. "We will work together to realise their dream of implementing sharia," said the Brotherhood contender, who himself spent time in jail under deposed leader Hosni Mubarak. An engineer with a doctorate from the United States, Mursi is a long-serving, influential figure in the Brotherhood, a movement outlawed under Mubarak but which won close to half of the seats in parliamentary elections held after his overthrow. Mursi was flung into the presidential race a month ago by the disqualification of Khairat al-Shater, the group's first-choice candidate, and has struggled to shake off the label as the Brotherhood's "substitute candidate". Like other Islamists in the race, Mursi has courted the ultra-orthodox Salafi Islamist movement which has emerged in the past year to challenge the Brotherhood's dominance - a factor some say helps to explain the hardening campaign rhetoric. The Nour Party, a Salafi group that won more than a fifth of the seats in the parliamentary vote, has endorsed Mursi's main Islamist rival, Abdel Moneim Abol Fotouh, who parted ways with the Brotherhood last year and has cast himself as a moderate. In a gesture to Gama'a al-Islamiya, another Salafi group, Mursi has pledged to work for the release of Sheikh Omar Abdel-Rahman, a militant preacher imprisoned in the United States in the 1990s for plotting attacks in New York. Abdel-Rahman is the spiritual leader of Gama'a al-Islamiya, which was involved in the 1981 assassination of President Anwar Sadat but renounced violence in 1997. The group has entered mainstream politics since Mubarak was toppled. Another cleric, the independent Safwat el-Hegazi, has added a radical flavour to Mursi's campaign, taking to the stage at his events to urge the creation of a Muslim super-state with Jerusalem as its capital and drawing enthusiastic chants from the crowds. Mursi's own speech-making style is stiff and formal. Critics say he lacks the charisma of some of the other candidates. Other Brotherhood leaders, Shater among them, have appeared alongside Mursi at campaign events, reinforcing the impression this is a presidential bid by a movement, not an individual. The son of a peasant, Mursi has spoken of a simple childhood in a village in the Nile Delta province of Sharqia, recalling how his mother taught him prayer and the Koran. He studied engineering at Cairo University and in 1978 went to California to complete his studies. He returned to Egypt in 1985. Two of his five children hold U.S. citizenship. Helmi el-Gazzar, a Brotherhood MP who has known Mursi for years, describes him as a scientific character with an analytical mind. "He was an indefatigable man, tangibly eager to perform the tasks for which he was responsible," Gazzar told Reuters, recalling his days working with Mursi in Cairo. Mursi's critics portray him as a Brotherhood apparatchik and part of a conservative clique within the group who has long been dismissive of other political forces in Egypt. "He feels they do not have roots in the Egyptian street," said Mohamed Habib, a former deputy Brotherhood leader, who left the group last year in protest at its post-Mubarak policies. Head of Freedom and Justice Party that the Brotherhood established last year, Mursi comes across as deeply committed to the 84-year-old movement. His daughter is married to the son of another Brotherhood leader and he has described his wife, who wears a long, cape-like headscarf, as a Brotherhood activist. Like other Brotherhood members, Mursi has sworn an oath of allegiance to the group, raising questions over whether that would outweigh his loyalty to the nation. Mohamed Badie, the Brotherhood's leader, has said that Mursi would be relieved of the oath if elected president.