Ayatollah Montazeri has emerged as the spiritual leader of the opposition, an adversary the state has been unable to silence or jail because of his religious credentials and seminal role in the founding of the republic…

“We have many intellectuals who criticize this regime from the democratic point of view,” said Mehdi Khaliji, a former seminary student in Qum and now a senior fellow at the Washington Institute for Near East Policy. “He criticizes this regime purely from a religious point of view, and this is very hurtful. The regime wants to say, ‘If I am not democratic enough that doesn’t matter, I am Islamic.’

“He says it is not an Islamic government.”…

While Iran’s current supreme leader, Ayatollah Ali Khamenei, has no special religious credentials, Ayatollah Montazeri is a marja, or source of emulation, the highest standing a cleric can hold in Shiite Islam. Not only that, he is the architect of Velayat-e Faqih, or guardianship of the jurist, the foundation of Iran’s theocracy and the source of the supreme leader’s legitimacy. Indeed, when Ayatollah Khamenei was a student, Ayatollah Montazeri was one of his teachers.

“He is able to delegitimize Khamenei more than anybody else on the Earth,” Mr. Khaliji said.