The diminutive and scrawny octogenarian is little known in the West, which he holds in contempt, but Ayatollah Ahmad Jannati wields considerable influence in Iran, where he is braying for the execution of pro-democracy protesters. A long-time bęte noire of the reformist movement, the white-bearded cleric is the veteran head of Iran's powerful Guardian Council, which screens candidates for national elections and has, notoriously, banned thousands in recent years for being too "liberal". Bills passed by parliament also have to be cleared by the hardline body of 12 jurists and clerics.
Ayatollah Jannati is in the limelight now as the leading radical voice who insists that Iran's post-election crisis can be controlled through brutal force. More pragmatic conservatives, however, see the need for compromise with the opposition as the best hope of dragging the regime out of its worst, self-inflicted crisis. But, proclaimed Ayatollah Jannati last week: If rioters are not dealt with firmly and strongly, the situation will become more serious in the future - "There is no space for tolerance." He cited the Quran and Islamic teachings to justify the execution of protesters.
The opposition's main leaders have made conciliatory statements in recent weeks. Despite their rejection of the presidential vote, they insist that they remain staunchly loyal to the Islamic Republic, but want an end to authoritarianism and force. For the disenchanted and angry electorate to accept any deal, the supreme leader, Ayatollah Ali Khamenei, would probably have to make a major concession, such as forcing the president Mahmoud Ahmadinejad to step down, analysts say. The president is anyway deeply unpopular with many pragmatic conservatives.
In turn, opposition leaders have made clear that they will strive to rein in their more radical supporters. "We do not want to make another revolution and do not seek the overthrow of the regime," Mehdi Karroubi, a candidate in June's elections and one of the opposition's most outspoken leaders, said in an interview with the Financial Times last week. He also criticised chants by some protesters who have called for an end to the Islamist government and who have lambasted the supreme leader.
Meanwhile, in an interview posted on a reformist website last Thursday, Mr Karrubi, a former parliamentary speaker, appeared to be transferring responsibility for the brutal post-election actions away from Ayatollah Khamenei to Ayatollah Jannati. "He [Jannati] says that claims of fraud are totally false and calls it a crime against the nation, but who does not know that he has committed crimes against the revolution, the blood of the martyrs, the imam and the dear people of Iran," Mr Karrubi said.
By targeting Ayatollah Jannati, Mr Karroubi may be hoping to give Ayatollah Khamenei the opportunity to reclaim his position as a neutral arbiter between the opposition and the regime's hardliners, some analysts say. The supreme leader, however, has given no signal that he is willing to compromise, while Ayatollah Jannati, who is close to both him and Mr Ahmadinejad, insists concessions will be seen as signs of weakness.
"Any time we show laxness we will suffer blows," he told Friday prayer worshippers last week in a typically fiery sermon. "When it comes to suppressing the enemy, divine compassion and leniency have no meaning." He went on to praise Iran's judiciary chief for the swift execution last week of two alleged members of a banned monarchist group and urged him "to execute others if they do not give up such protests".
The two men, who were hanged at dawn last Thursday, were convicted of being enemies of God and plotting to topple the Islamist regime. But Iran's opposition, which condemned the executions, said the men had been arrested months before the June vote and were not involved in the post-election street protests. Nine other people have been sentenced to death over the unrest, the judiciary said. The executions, the first of alleged activists since the June vote, were seen as an attempt to deter people from attending huge protest rallies on the February 11 anniversary of Iran's 1979 Islamic revolution.
Iran's political crisis now appears set to deepen. On Saturday, the judiciary put another 16 alleged protesters on trial while Mr Karrubi and Mir Hossein Mousavi, a former prime minister and the man millions of Iranians believe was the true winner of June's elections, defiantly called on demonstrators to take to the streets on February 11. The Revolutionary Guard warned that anyone not involved in official rallies would be "firmly confronted".
Mr Karroubi and Mr Mousavi have also rounded on Ayatollah Jannati over his lurid calls for the harsh treatment of protesters. "It is regrettable to see the Friday prayers tribune has turned into a venue for inciting violence and encouraging more executions," the two opposition leaders were quoted as saying. The remark came in an account of a recent meeting between the two reformist leaders that was posted on Mr Mousavi's Facebook page and on Mr Karroubi's news website.
Aside from the Guardian Council, Ayatollah Jannati, who speaks Arabic as well as his native Farsi, holds political office in two other important bodies. He is on the Assembly of Experts, which selects and advises the supreme leader and which technically has the power to remove him. And he is a member of the Expediency Discernment Council, which serves to resolve disputes between parliament and the Guardian Council.
He was also one of the founders of the Haqqani seminary, which teaches that Islam and democracy are incompatible. The Ahmadinejad government has endowed the seminary - one of Qom's most prestigious theological schools - with generous subsidies. Many of its former students occupy senior positions in Iran's security and judicial establishment. By some accounts, Ayatollah Jannati also created the feared Ansar Hizbollah vigilante militia, which over the years has attacked reformist students and served as motorcycle-riding shock troops used to crush street protests.
Farideh Farhi, a leading Iran expert at the University of Hawaii, said in an interview: "Jannati represents the most extremist thought in Iran, always calling for a forceful and non-accommodating approach to any form of dissent in the Islamic Republic." Diatribes against the West also frequently pepper his Friday prayer sermons. He once branded Bill Clinton, the former US president, as a "sexual sadist" and accused him of "moral decadence". On another occasion, Ayatollah Jannati said: "The British are the worst con men, the most devious people and they are foxier than everyone else."