Mr Mahmoud Ahmadinjad's decisive victory in Iran's presidential election sends a radical message about divisions in its society and the country's relations with the rest of the world.
This matters because of Iran's size and strategic importance in the Middle East. He stood on an egalitarian platform inspired by the ideals of the 1979 Islamic revolution and was supported by fundamentalist activists and the country's religious leadership. His defeat of the veteran pragmatist Ayatollah Akbar Hashemi Rafsanjani is another blow to the country's ineffective reformist movement after last year's parliamentary elections and concentrates power in the hands of its Islamic opponents.
As mayor of Tehran since 2003 Mr Ahmadinjad has lived modestly and established a reputation for honest and effective administration - rare virtues in a country which suffers from widespread corruption, widening gaps between rich and poor and an opaque system of government dominated by a clerical establishment. His supporters made the most of his appeal to workers, farmers and youth who have not shared in Iran's wealth, in addition to religious voters impressed by his credentials.
His victory is nonetheless a surprise, since he came very much from behind and was a little known figure. His 17 million votes to Rafsanjani's 10 million in a 63 per cent turnout gives him a legitimacy which overrides flaws in the election in which candidates were vetted by clerical groups and there were allegations of fraud.
Mr Ahmadinjad has promised to redistribute wealth from the oil industry, a concerted campaign against corruption and is pledged to continue and intensify Iran's nuclear power programme. As mayor he clamped down on western style advertising in Tehran and during the campaign said he will oppose "westoxification". Secular Iranians fear he will attack the limited social freedoms established in recent years, including how women wear the hajib. They will watch with interest to see whether he lives up to his statement that "the country's true problem is employment and housing, not what to wear". Jobless rates are very high among the young people under 30 who make up more than 50 per cent of Iran's 60 million people. They will now have high expectations of change after the failure of the cautious reformist movement to make a real difference to their lives. The stakes are high and his chances of success limited by the fragmentation of political power and resistance from vested interests.
Internationally Mr Ahmadinjad's victory will make it more difficult to reach agreement on limiting Iran's nuclear power programme so as to prevent it developing a nuclear weapons capacity. The prolonged negotiations involving France, Britain and Germany have failed to resolve the issue. Neoconservatives in the Bush administration will welcome this result as further evidence that Iran must be contained rather than engaged. Agreement will certainly not be reached unless the US is willing to support the European efforts. If the talks collapse the prospect for tension and instability will increase, alongside the deepening problems in neighbouring Iraq.