TEHRAN — With the death of Ayatollah Ali Akbar Hashemi Rafsanjani on Sunday, Iran’s political factions knew immediately that any space by reformers to maneuver had just significantly decreased.

Change had come, and it did not favor those seeking to turn Iran into a less revolutionary country with more tolerance and outreach to the West — especially the United States.

Mr. Rafsanjani, a former president who helped found the Islamic republic, had been the one man too large to be sidelined by conservative hard-liners. Now he was suddenly gone, dead from what state media described as cardiac arrest — and with no one influential enough to fill his shoes.

Iran’s long-marginalized reformists and moderates, who would use Mr. Rafsanjani’s regular calls for more personal freedoms and requests to establish better relations with the United States to advance their political agendas, suddenly felt exposed and weakened.

Who would now warn publicly against “Islamic fascism,” when the hard-liners sought to influence elections? Who would state openly that there should be a nuclear compromise?

Mr. Rafsanjani said things others would not dare to say, all agreed, and his voice had at least created some tolerance for debates.

“Hard-liners will be happy, but this is the start of a period of anxiety for many,” said Fazel Meybodi, a cleric from the holy city Qum who supports reforms in Iran. “His death disturbs the fragile balance we had in Iran.”

There simply are no replacements for Mr. Rafsanjani, analysts from all factions say.

His death also reflects the dwindling number of leaders from the generation that overthrew the shah nearly four decades ago. Most are now in their 80s or even older.

“It is a very powerful reminder that Iran is at the beginning of a major leadership transition that will play a very psychological role in Iran’s politics,” said Vali R. Nasr, a Middle East scholar who is dean of the Johns Hopkins School of Advanced International Studies.

“I think this in some ways rattles Iran’s political system, in that it underscores the fact that with everything else going on — Syria, the nuclear deal — there will be a passing of the baton to the next generation,” Mr. Nasr said.

Two of Mr. Rafsanjani’s most important protégés — Hassan Rouhani, the current president, and Mohammad Khatami, a former president — both owe their political careers to him. But Mr. Rouhani, up for re-election this year, is fighting for his political life. Mr. Khatami, who has been sidelined by conservative adversaries for years, is now even weaker.

Mr. Rouhani managed to create a coalition to win the elections in 2013, with Mr. Rafsanjani’s support. Having successfully negotiated a nuclear agreement with the United States and other big powers, partly from encouragement by Mr. Rafsanjani, Mr. Rouhani promised a bright economic future for Iran — which has yet to happen.

With the demise of his mentor and protector, Iran’s president will find it hard to gather the same level of support he received four years ago with the backing of Mr. Rafsanjani, analysts say.

“He was a very powerful figure for Mr. Rouhani to rely upon,” said Mohammad Marandi, a professor at Tehran University who is close to Iran’s leaders. “Many worked with him because of that support. The passing of Mr. Rafsanjani complicates the president’s position and makes his re-election less certain.”

Mr. Khatami won presidential elections in 1997 after having received Mr. Rafsanjani’s support, and led Iran through an era of greater personal freedoms and Western outreach that was quashed by unelected, hard-line centers of power.

“It is Mr. Khatami who should take on the burden of the late Ayatollah Hashemi Rafsanjani’s responsibility,” said Mohammadreza Shamsolvaezin, a former reformist politician and activist. But Mr. Khatami is all but paralyzed politically. The hard-line-dominated judiciary has ordered all Iranian media not to carry his picture or even quote his website. Besides appearances at theater plays, religious gatherings and art exhibitions, Mr. Khatami has remained silent.

Mr. Rafsanjani could speak more freely than others, not only because of his revolutionary credentials, but also because of his friendship with Ayatollah Ali Khamenei, whom he helped become supreme leader in 1989.

Ayatollah Khamenei, who has skillfully played all Iranian factions, would never go as far as to completely isolate Mr. Rafsanjani, even when he supported protests that followed the disputed 2009 presidential election. While the presidential candidates Mir Hossein Mousavi and Mehdi Karroubi were placed under house arrest in 2011 for their criticisms, Mr. Rafsanjani was stripped of several functions but never purged.

In a statement, Ayatollah Khamenei lamented the passing of Mr. Rafsanjani. Still, it was clear to many that Ayatollah Khamenei regarded him not only as a friend but a rival, whose absence could now make the role of supreme leader even more powerful.

“The loss of a comrade and ally, with whom I share a friendship that dates back to 59 years ago, is difficult and heart-rending,” said a statement posted on Ayatollah Khamenei’s website on Sunday. He also referred obliquely to their disagreements.

“Differences in views and interpretations of Islamic law in various points of this long time could never break the friendship,” the statement said. “After him, I cannot think of anyone with whom I share such long history and experience along the highs and lows of historical moments.”

Hard-liners joined in on the mourning, giving public statements of condolence, but with the realization that the political wind in Iran would now blow even more in their favor.

For them Mr. Rafsanjani had been a wild card, who could evoke rulings from the founder of the Islamic republic, Ayatollah Ruhollah Khomeini, that would oppose their rigid narrative of isolation and anti-Westernism. Mr. Rafsanjani was especially dangerous, they said, because of his conviction that Iran had changed and that establishing relations with the United States was the only way to secure the future of the Islamic republic.

Mr. Rafsanjani also had cordial ties with the leaders of Saudi Arabia, Iran’s principal rival in the Middle East, who share a mutual hostility with Ayatollah Khamenei.

Hard-liners also have faulted Mr. Rafsanjani for having founded a chain of affordable universities during the reconstruction that followed the 1980-88 Iran-Iraq war. Some conservatives now blame these schools for having helped sow what they regard as the dangerous modernist aspirations of Iran’s middle class.

Many conservatives in Iran also suspected Mr. Rafsanjani of having used his contacts to undercut Ayatollah Khamenei on issues where Ayatollah Khamenei would choose ideology over diplomacy. Mr. Rafsanjani preferred pragmatism and change to keep the ruling system in power.

“The invisible hands of the late Ali Akbar Rafsanjani are gone,” said Hamidreza Taraghi, a hard-line political analyst who has close relations with many of Iran’s top leaders. “This means an end to secret meetings by reformists and moderates seeking closer ties with America; from now on we can make decisions much easier and with more coordination.”

Source: NYTimes