The head of the Greek Orthodox Church, Archbishop Christodoulos, has died, aged 69, after suffering from cancer.
Archbishop Christodoulos was a popular public figure in Greece
An attempted liver transplant in 2007 was unsuccessful, and the archbishop had grown steadily weaker recently.
Archbishop Christodoulos was a colourful and controversial figure, the BBC's Malcolm Brabant in Greece says.
He defended the church's pre-eminent role in the state and upheld Hellenism - the national character and culture of Greece, our correspondent says.
But critics say that under Archbishop Christodoulos, Greece remained a country which discriminates against those who are not Orthodox, including Catholics and worshippers of other branches of Christianity.
'Lost will to live'
The archbishop of Athens and all Greece died at his Athens home early on Monday, church officials said.
They said he had refused hospital treatment in the final weeks of his life.
"He lost the will to live", deciding to "give up his soul", Bishop Anthimos of Salonika told Greece's state television NET.
Archbishop Christodoulos was diagnosed with cancer of the liver and large intestine in 2007. He was then treated in the US for 10 weeks, but a liver transplant operation last October was aborted as the cancer had spread.
Senior Greek Orthodox clergy began arriving at the archbishop's home soon after his death was announced.
The archbishop's flag-draped coffin was later taken to Athens' cathedral, where his body will lie in state until the funeral on Thursday.
A four-day period of mourning has been declared in Greece.
Greek Prime Minister Costas Karamanlis paid tribute to the archbishop, describing him as "an enlightened hierarch whose pastoral work brought the church near the society and contemporary problems".
The Holy Synod, the church's top decision-making body, will hold a meeting later on Monday. It has 20 days in which to elect the archbishop's successor.
Elected as church leader in 1998, Archbishop Christodoulos was known as a fierce and outspoken defender of Greece and the role of the Orthodox Church within it, our correspondent says.
Archbishop Christodoulos paid a historic visit to the Vatican in 2006
The archbishop once said that when ancient Greeks were creating the lights of civilisation, Europeans were living in trees.
He said Greeks lived in paradise compared to other Europeans because they had a strong faith, built churches, followed traditions and resisted globalisation.
Archbishop Christodoulos opposed Turkey's efforts to join the European Union, describing the Turks as barbarians, our correspondent says.
The archbishop clashed with the Greek government when the authorities wanted to remove religious status from identity cards.
"They are trying to take away our society's Christian and Orthodox identity, using various groundless arguments, because they hate God and want to marginalise the Church," he said.
He said it was a part of a plan to separate church and state, dreamed up by neo-intellectuals who wanted to attack Orthodoxy and tear at its flesh.
In 2001, the archbishop incurred the wrath of ultra Orthodox believers when he met the late Pope John Paul II in Greece.
In 2006, he met Pope Benedict XVI at the Vatican, as part of efforts to bring the two churches together - the first such talks between Greece's most senior cleric and the leader of the world's Roman Catholics.
Their meeting focused on attempts to end the Great Schism that dates from 1054.
The Greek Orthodox Church is an autocephalous, or ecclesiastically independent, branch of the Eastern Orthodox Communion, covering the territory of Greece.