For years, he was the faithful party member, a favoured disciple of Iran's first Supreme Leader, Ayatollah Ruhollah Khomaini. But something happened to Mir-Hossein Mousavi, this paragon of the Islamic Revolution, that led him to declare this weekend that he was "ready for martyrdom" in his fight against the regime of Iran's current Supreme Leader.
"Don't let the liars and fraudsters steal the flag of defending the Islamic regime from you," he told his followers in a powerful statement issued Sunday. "Don't let the delinquents and the strangers confiscate from you the precious heritage of the Islamic Revolution, which is built from the blood of your honest fathers."
"Be confident," he added, "that I will stand by your side at all times."
This is Mr. Mousavi's last hurrah, says Saeed Rahnema, an Iranian-born political scientist at York University in Toronto. "If he backs down now, he's finished forever."
"He says he's willing to die for the cause," Mr. Rahnema said, "because he has nothing to lose."
That wasn't the way Mr. Mousavi's career began.
Raised in the town of Khameneh, birthplace of today's Supreme Leader, Ayatollah Ali Khamenei, Mr. Mousavi is the grandson of the Ayatollah's paternal aunt, which makes the two men cousins.
It is said that from his youngest days Mr. Mousavi always put religion first, becoming active in various Islamic societies while at university in the 1960s and specializing in traditional Islamic architecture when he took his master's degree.
One of his architecture students in the 1970s complained that as a professor he was too religious for her liking, though she now supports his campaign.
By the late seventies, Mr. Mousavi was one of the founders of the Islamic Republican Party, which supported the establishment of a theocracy in Iran and became a major force in the new republic.
Ayatollah Khomaini, who returned to Iran from exile in 1979, appointed the 37-year-old Mr. Mousavi editor of the party's newspaper Jomhouri-e Eslami (Islamic Republic). From that prominent platform he served as the leader's mouthpiece, spearheading the fight against the country's moderate first president Abolhassan Banisadr, who eventually fled to France in 1981.
It was a time of intrigue and political manipulation in Iran. The man who succeeded Mr. Banisadr as president, Mohammad-Ali Rajai, served only 15 days before he was assassinated. After him came Ali Khamenei, now Supreme Leader.
Mr. Mousavi's fortunes only grew.
Appointed foreign minister in the summer of 1981, by the end of the year he was prime minister. (The president's first choice for the office was emphatically rejected by parliament, which was chaired by Ali Akbar Hashemi Rafsanjani. Mr. Mousavi was an acceptable compromise.) Taking office 15 months after the outbreak of the Iran-Iraq war, Mr. Mousavi would be known as the wartime prime minister, effectively handling the economic and labour shortages imposed by the conflict. But for many, he would best be remembered as the man who led Iran's "Cultural Revolution," purging universities of their Western-trained faculty.
I [like many others]was thrown out of the university that Mousavi helped to shut down," said Azar Nafisi, author of Reading Lolita in Tehran .
Of course, Americans inside the Reagan administration will remember Mr. Mousavi for another reason: He was their go-to guy in the Iran-contra escapade. This was the illegal scheme concocted by Oliver North and others to have Israel supply weapons to Iranians, paid for by Washington, in exchange for the release of American hostages in Lebanon and payments to the contra rebel group in Nicaragua.
Britons will recall that he was the Iranian leader who severed ties with the United Kingdom for its refusal to disavow author Salman Rushdie, whose book The Satanic Verses earned him a death fatwa from Ayatollah Khomaini, Mr. Mousavi's mentor.
Dutiful he may have been, but in 1989, when Ayatollah Khomaini died and Ayatollah Khamenei succeeded him, Mr. Mousavi found himself out of favour and withdrew from public life. He returned to teaching and the arts.
But was he a recluse, or was he quietly plotting?
As the 1997 presidential election approached, Mr. Mousavi indicated he intended to be a candidate; until, that is, a conversation with the outgoing president, Mr. Rafsanjani, who encouraged him to step aside in favour of Mohammad Khatami. Again, in 2005, Mr. Mousavi made noises about running, but deferred once more to Mr. Rafsanjani, who decided to run again. (He would lose in a runoff to Mahmoud Ahmadinejad.) This year, Mr. Mousavi was determined to run, and it was former president Khatami who pulled out of the race and supported him.
That was when the Mousavi campaign came to life.
Women's rights groups, youth and student movements and other civil society organizations that had been created during the Khatami presidency swung behind Mr. Mousavi.
To be sure, Mr. Mousavi strongly endorsed equal rights for women and he advocated reining in police powers. But rights advocates such as Noushin Ahmadi Khorasani say their support for his campaign was much more about the cause of liberty than about the candidate himself.
So at what point in this revolutionary's career did he decide to put his life on the line?
The seeds were planted 30 years ago, Prof. Rahnema said. "He was definitely a significant figure during the revolution and its immediate aftermath," he said. "But after that, he was a forgotten man."
Then, after years of being passed over as a presidential candidate, "he finally had a chance to redeem himself," Prof. Rahnema said.
Now, he's put everything on the line.
"I think he may be hoping that some kind of negotiations will spare him from a deadly showdown," Prof. Rahnema said. "But these days, you never know."