His followers have begun calling him “the Gandhi of Iran”. His image is carried aloft in the vast Opposition demonstrations that have shaken Iran in recent days, his name chanted in rhyming verses that invoke Islam’s most sacred martyrs. Mir Hussein Moussavi has become the public face of the movement, the man the protesters consider the true winner of the presidential election.

But he is in some ways an accidental leader, a moderate figure anointed at the last minute to represent a popular upwelling against Mahmoud Ahmadinejad. And it is not yet clear how far he will be willing to go in defending the broad democratic hopes he has come to embody.

Moussavi, 67, is an insider who has moved toward opposition, and his motives for doing so remain murky. Some prominent figures have rallied to his cause, including former President Ali Akbar Hashemi Rafsanjani. It is not clear how much this battle reflects a popular resistance to Ahmadinejad’s hardline policies, and how much is about a struggle for power.

Moussavi began his political career as a hardliner and a favourite of Ayatollah Ruhollah Khomeini. Although he has long had an adversarial relationship with Iran’s current supreme leader Ayatollah Ali Khamenei, his insider status makes him loath to mount a real challenge to the core institutions of the Islamic republic.

“He is a hybrid child of the revolution,” said Shahram Kholdi, a lecturer at the University of Manchester who has written about Moussavi’s political evolution. “He is committed to Islamic principles but has liberal aspirations.”