Patriarch Alexiy II has passed away.
President Dmitry Medvedev, who was on an official visit to India, hailed the patriarch as "an outstanding religious figure" and canceled a planned trip to Italy to return to Moscow.
"He was a true shepherd, who throughout his life was an example of spiritual fortitude and noble human deeds," Medvedev told state television. "He was always with his flock both in the days of reprisals and in the period of religious revival."
Prime Minister and former President Vladimir Putin, an ex- communist spy who now openly professes his Orthodox faith, said Alexiy was a "great statesman" who had "done a great deal for the establishment of a new Russian statehood."
The Church never commented on Alexiy's health and gave the cause of death as heart failure. But diplomats in Moscow had said the Patriarch had been suffering from cancer for some time.
In a sign of his importance, Russian state television immediately ran a film showing highlights from Alexiy's life, accompanied by the sound of tolling church bells.
Church officials said Metropolitan Juvenali of Krutitsy and Kolomna -- a senior bishop -- may lead the Russian Orthodox until the election of a new patriarch.
Patriarch of Moscow and All Russia since 1990, the Estonian-born Alexiy was a powerful and influential figure with close links to the Kremlin but a controversial past and strongly held conservative views on social issues.
He oversaw a major religious revival in Russia after the collapse of the Soviet Union, with hundreds of new churches built across the country, monasteries reopened and seminaries filling with new priests.
He was clearly a man of great faith, and I'm sure will be received graciously by God.
Whenever a great religious leader dies, it is a reminder that life is, ultimately, short, and that leading or belonging to a particular faith is not assurance of what is to come, or the length of one's years.
It is also a reminder that unfinished business is unfortunate. One of the greatest wounds I witnessed was the Patriarch's coldness to the very kind Pope John Paul II. I had hoped that the Patriarch would make better intentioned progress with Pope Benedict XVI, but live and learn, as I said, take care of one's business before you are called to meet your Maker.
Rest in peace and sincere condolences to his flock.