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?"
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.
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.
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.
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.