DUBAI (Reuters) - President Mahmoud Ahmadinejad's nationalist protégé Esfandiar Rahim Mashaie is one of the most divisive men in Iran, and if he is allowed to stand in June's presidential election, it would be a direct challenge to the authority of the supreme leader.
Mashaie brought to an end years of speculation on Saturday by registering as a candidate in an election that Supreme Leader Ayatollah Ali Khamenei hopes will usher in a period of much needed calm and unity.
But Mashaie's candidacy has the potential to tear apart the already strained political divisions between non-clerical populists, like him and Ahmadinejad, and loyal lieutenants of the Islamic theocracy, just four years after Iran was rocked by widespread protests over Ahmadinejad disputed re-election.
"Unlike the first generation of revolutionary elite who played by the rules, the Ahmadinejad group has consistently pushed against regime red lines and at times even challenged the authority of the supreme leader," said U.S.-based expert on Iran's electoral system, Yasmin Alem.
"For them, ambition trumps allegiance to the regime's principles."
Khamenei is supposed to be above the fray of every day politics, but personally intervened in 2009 to stop Ahmadinejad making Mashaie his first vice president.
Ahmadinejad was not completely cowed though and instead made Mashaie his chief-of-staff. For Mashaie to now run for president after Khamenei has shown his disapproval is an affront to the leader's authority, a cornerstone of the Islamic Republic.
"Allowing Mashaie to run for office would undermine the credibility of Iran's supreme leader," Alem said. "I think both Ahmadinejad and Mashaie are sly enough to know this."
The Ahmadinejad camp has also tested the nerves of "principlists" - those who profess total loyalty to the supreme leader - with their slogan of "long live Spring", which many have read as a coded call for political change.
But like all candidates, Mashaie first has to get through the vetting process by the Guardian Council - a group of 12 clerics and jurists responsible for overseeing the election.
"If Mashaie is barred, it might prompt Ahmadinejad to take action that would be destabilizing," said Mohammad Shabani, an Iranian analyst based in London. "Regardless of whether Mashaie is approved as a candidate, his candidacy is bound to be fateful."
While loyalists lose sleep over a possible Mashaie presidency, others are not sure the 52-year-old can win.
"I don't see a Mashaie presidency at this stage," said a Western diplomat based in Tehran. "He's a dark horse but my best guess is he'll be barred from contention."
Mashaie grew up inside the murky politics of the Islamic Republic, joining the intelligence ministry in the 1980s and serving in Iran's Kurdistan province where he met Ahmadinejad.
He rose to prominence when Ahmadinejad, at that point a little-known mayor of Tehran, astonished the Iranian nation by winning the presidency in 2005. They came even closer when Mashaie's daughter married Ahmadinejad's son in 2008.
A background figure in the cabinet, Mashaie shot to notoriety in Iran the same year when he said Iran was a friend of the people in the United States and Israel, which incurred the wrath of hardline clerics and politicians alike.
Since the Islamic Revolution, Iran has held a deeply hostile stance against what it calls "the Zionist regime" and has levied considerable support and encouragement for Palestinian groups.
But perhaps Mashaie's greatest sin in the eyes of the conservative establishment was to involve himself in religious debate, traditionally the preserve of clerics in Shi'ite Islam.
"Without Iran, Islam would be lost," Mehr news agency quoted him as saying in 2010. "Countries are scared of Iran, because the truth of Islam is here."
Comments like those and others indicate Mashaie is seeking "a reorientation of Iranian state identity", Shabani said. "One way of doing this is to seek to end the clerical monopoly on promulgation of the nature of Iran's Islamic identity."
Clerics have also blasted Mashaie and Ahmadinejad for making "seditious and erroneous" comments about the Mahdi, the holy saint who Shi'ite Muslims believe will return to re-establish the rightful governance of Islam.
Regardless of the pressure, the president has stood by him.
"Ahmadinejad's unconditional devotion to Mashaie is no secret," Alem said. "While neither man has shied away from letting their unbreakable bond become public, the exact nature of their relationship is suffused in mystery.
"His political outlook is an amalgam of nationalistic and Messianic beliefs," she said.
For the past eight years, Ahmadinejad and Mashaie, who was previously head of Iran's cultural heritage organization, have fine-tuned a strongly nationalist doctrine that analysts say is increasingly popular among young and secular groups and those tired of their leaders' incessant Islamic rhetoric.
Iranians are deeply proud of their pre-Islamic traditions and heritage and the two have strived to harness such symbols.
Perhaps the most blatant example of the new doctrine was the loan by the British Museum to Tehran of the Cyrus Cylinder - a pre-Islamic, 2,600 year old clay antiquity that scholars regard as the "first bill of human rights".
"That was the one thing they wanted to borrow," said British Museum director Neil Macgregor in an interview with CNN.
Ahmadinejad attended the cylinder's Tehran unveiling in 2010, a move that would have been inconceivable for previous presidents. But Mashaie's central role in the affair stands out.
"Mr Mashaie began talking about Cyrus as a forerunner of the prophet (Mohammad), as also embodying values that can be part of an Islamic tradition," Macgregor said in the interview.
Linking the prophet with a pre-Islamic imperialist Persian monarch does nothing but stoke further fears among the Islamic Republic's old guard about Mashaie's intentions.
Editing by Jon Hemming