If anyone embodies the reason why the nuclear showdown with Iran sends shivers through Western capitals, let alone the country's Arab neighbours, it is Mahmoud Ahmadinejad.
The bearded 49-year-old's election as Iran's president last summer took millions of Iranians, as well as the rest of the world, by surprise. Since then he has caused outrage by demanding that Israel be "wiped off the map", questioning the historical authenticity of the Holocaust, and saying that if Europe and America wanted to atone by giving the Jews a homeland, it should be on their territory: "Why should the innocent nation of Palestine pay for this crime?"
Chilling words from the leader of a country which seems to be bent on confrontation with the international community over its nuclear programme. He adheres to the official line that this is for peaceful purposes - although Iran, a major oil producer with natural gas reserves second only to Russia's, has never explained why it needs nuclear power - and dismisses foreign criticism as "noise". The major powers, Ahmadinejad said in a televised speech last week, were "a group of bullies" trying to deprive Iran and other nations of their "legal and natural rights".
The alarm caused by the president's intemperate rhetoric is increased precisely because so little is known about him. Some of the Americans held hostage in the US embassy in Tehran for 444 days between late 1979 and early 1981 have claimed that he was among their captors. He has also been accused of involvement in the assassinations of exiled Kurdish politicians in Austria, and executions of political prisoners in Tehran's notorious Evin prison.
President George Bush has ordered an investigation into the hostage-taking claim, although acknowledged leaders of the embassy siege have denied that he had anything to do with the crisis. He and the Iranian government have dismissed all the allegations against him as a smear campaign by the US and "Zionist media".
More worrying for some is that Ahmadinejad is closely identified with the cult of the "hidden imam", the 12th and last of the line of imams revered by Shia Muslims. In a clear parallel with Jewish and Christian visions of Armageddon, Shias believe the imam zaman will return at a time of great turmoil to defeat the forces of evil; recently the president urged Iranians to work hard for this moment. As one commentator pointed out, this was like Tony Blair telling Britons to prepare for the Second Coming.
The most extreme zealots, a group called the Hojjatieh, say total chaos should be created to hasten the coming of the Mahdi, and there have been claims that Ahmadinejad, if not a member, sympathises with them. This explains his reckless attitude, say his critics. If the final triumph of Islam can be brought closer by provoking a nuclear war with Israel or America, why hold back?
It might be possible to dismiss this as scaremongering if it were not for a DVD circulating in Iran which shows the president in conversation with a conservative ayatollah. Ahmadinejad is speaking about his defiant address to the UN General Assembly last autumn, in which he refused to back down on Iran's nuclear programme.
"One of our group told me that when I started to say 'Bismillah Muhammad', he saw a green light come from around me, and I was placed inside this aura," he says. "I felt it myself. I felt the atmosphere change, and for those 27 or 28 minutes, all the leaders of the world did not blink. When I say they didn't move an eyelid, I'm not exaggerating. They were looking as if a hand was holding them there."
So who is Mahmoud Ahmadinejad, and how did he manage to win the presidency? He was unknown when he was elected mayor of Tehran in 2003, with all but 12 per cent of voters staying away from the polls. The son of a blacksmith from Aradan, south of Tehran, he performed well enough in his studies to gain a PhD in engineering and urban management at the Iran University of Science and Technology, but his speech and appearance remain working-class. His only declared assets are said to be a 30-year-old Paykan car, the Iranian version of the old Hillman Hunter, and a small house.
The president's ascetic image is reinforced by his rumpled suit and open-necked shirt, the uniform of the generation which overthrew the Shah and brought the late Ayatollah Khomeini to power (it is a mark of Iran's difference that hip young men in Tehran seek to annoy their elders by wearing ties).
When he was mayor, he tried to bring back strict Islamic standards of behaviour, with little success. The sophisticates of north Tehran mocked his accent, and dismissed his decision to run for president, while the religious establishment backed another conservative.
Everybody, including diplomats and the foreign press, expected the former president, Ali Akbar Hashemi Rafsanjani, a worldly cleric, to win, and he duly took first place among the seven candidates in the first round. But Ahmadinejad came second, and won the run-off. What neither the Tehran elite nor the mullahs realised was how unpopular they were: most of the victor's votes came not from religious zealots, but from the struggling masses who responded to his uncorrupt image, and his promise to "put Iran's oil wealth on people's tables".
The realities of office have been another matter. Alongside the formal trappings of the presidency, cabinet and parliament is the theocratic power structure, presided over by the Supreme Leader, Ayatollah Ali Khamenei, who took over on Khomeini's death. The decisions on most matters, including nuclear development, are with him.
Powerful economic interests are also ranged against the president - his plan to redistribute oil revenues has hit trouble, because it is seen as inflationary. He sacked the entire cabinet on taking over, but parliament rejected four nominees for the crucial job of oil minister, and the man eventually appointed was previously the deputy minister.
"Ahmadinejad promised a lot, but he can't deliver," said Dr Ali Granmayeh, a former Iranian diplomat now with the School of Oriental and African Studies at London University. "Some people think he is striking attitudes on the Holocaust and the nuclear question precisely because he has so little control over domestic policy."
There are even predictions that parliament could use its constitutional powers to dismiss Ahmadinejad before he has served a year. But the president's opponents will have to tread carefully: he has a popular mandate; they do not. However much the the world might want Iranians to get rid of their turbulent figurehead, we might have to put up with his tirades for some time.