THE post-election standoff in Iran has pitted two cousins and long-time rivals against each other in a renewed personal and political battle almost as old as the Islamic Republic itself. But the career trajectories of Mir Hossein Mousavi, the reformist leader, and Ayatollah Ali Husseini Khamenei, the country's supreme leader, have carried them in diametrically opposed directions.

Mousavi, 67, represents the hopes of Iran's reformists, a loose coalition committed to social justice and equality, increased freedom of expression, and rooting out endemic government corruption. During the campaign, Mousavi expressed determination to transform Iran's “alms-based economy” and reverse the country's “extremist” image abroad.

But as prime minister from 1981 to 1989, he had a reputation as a hardline radical who was close to Ayatollah Ruhollah Khomeini, the theocratic leader of the 1979 Islamic revolution. In contrast to his present-day support for social renewal and a mixed economy, the “old” Mousavi backed the system of extensive state control favoured by his mentor.

According to a regional analyst, Ranj Alaaldin, Mousavi was complicit in the 1979-81 US embassy hostage crisis, once belonged to Hezbollah's leadership council, and was the man who initiated Iran's nuclear programme.

In his two terms as president from 1981 to 1989, Khamenei, 69, was known as an economic liberal and a proponent of a stronger private sector. He also presided over the decision in July 1988 to sue for peace with Saddam Hussein's Iraq after eight years of war — a controversial move engineered by the then Majlis (parliament) speaker, Ayatollah Hashemi Rafsanjani, which Mousavi reportedly opposed.

But in his later incarnation as supreme leader, a post he took up after Khomeini's death in 1989, Khamenei has emerged as an arch-conservative, a sort of Persian neocon with strong anti-western views. He secured the chairmanship of the powerful guardian council for a key ally, Ayatollah Ahmad Jannati, opposed moves to liberalise press laws and social codes, and ordered a tough crackdown on a previous bout of student unrest in 2003.

Crucially, Khamenei was responsible for the second-round presidential election victory in 2005 of Mahmoud Ahmadinejad, and was quick to endorse the incumbent's contested landslide win on Friday. Despite his constitutional obligation to stand above the fray, Khamenei quietly tipped the balance in favour of Ahmadinejad over his old sparring partner, Rafsanjani.

He strongly supports Iran's “nuclear rights” and had been lukewarm in his response to Barack Obama's diplomatic overtures.

As the two leading political players under Khomeini, Mousavi and Khamenei were renowned for their frequent policy clashes on economic management, the conduct of the Iraq war, and the extent to which Iran should open up to western companies when post-war reconstruction began. Mousavi was usually the winner because he had the ear and the support of Khomeini.

After his re-election as president in 1985, Khamenei made it clear that he did not want Mousavi to continue as prime minister, but was unable to force him out. In 1988, when yet another row escalated over cabinet appointments, Mousavi seemed to have had enough and tendered his resignation. It was thrown back in his face by Khomeini, who reportedly told him and Khamenei to stop squabbling and get on with the job.

These disagreements generated a degree of personal animosity that has continued to the present day, said Ali Ansari, an Iran expert and author.

“As prime minister Mousavi used to ignore Khamenei a lot and do his own thing. There's definitely a personal element,” said Ansari. Khamenei eventually asserted his authority in 1989 when, as newly installed supreme leader, he abolished the post of prime minister and pushed Mousavi into the political wilderness.

Mousavi subsequently took up teaching and was an adviser to Rafsanjani, during his presidency, and to Mohammad Khatami, the reformist president who preceded Ahmadinejad. During this period, lasting almost 20 years, his radical opinions appear to have gradually moderated as he moved towards the political centre. “His social and cultural views were really quite grim [when he was prime minister],” Ansari said. “Coming into the campaign he was well aware of that reputation and tried to soften it. He seems to have been influenced by his wife, Zahra Rahnavard. She is fairly liberal.”

Rahnavard broke with tradition by campaigning beside her husband and holding hands with him in public. Many analysts have attributed Mousavi's popularity among younger voters to her willingness to challenge taboos. All the same, Mousavi had remained an “establishment man” and was backed by other insider figures such as Rafsanjani, Ansari said.

In the event that the divisive Ahmadinejad were to be dropped and Mousavi become president, the latter's 25-year-long battle with Khamenei can be expected to resume in earnest. That is a strong reason for Khamenei to fight hard to keep him out. But while the warring cousins differ sharply on social issues, there may be more room for an accommodation than many suspect.

— The Guardian, London