When he resigns from the papacy on February 28, Pope Benedict XVI will become the first pontiff since Gregory XII in 1415 to walk away from the post, rather than die in it.
In today's world, "subject to so many rapid changes and shaken by questions of deep relevance for the life of faith", he told his cardinals yesterday, strength of mind and body were required to fulfil the ministry that had been entrusted to him on April 19, 2005.
Now he had "come to the certainty that my strengths, due to an advanced age, are no longer suited".
Among Muslim leaders he will perhaps be remembered as the pope whose heart was in the right place when it came to interdenominational harmony, but whose words sometimes let him down.
"Inter-religious dialogue," as he would later proclaim, was an essential part of the Roman Catholic Church's "commitment to the service of humanity" in a modern world defined by the mass movement of peoples, whether as refugees or migrants, and the Pope was soon making positive overtures towards Islam.
But the first serious test of his doctrine of Inter-religious dialogue came in September 2005, when the Danish newspaper Jyllands-Posten published its infamous cartoons depicting the Prophet Mohammed.
For some, Pope Benedict's response was slow in coming - and when it did arrive it was insufficiently unequivocal.
It was February 2006, as the controversy over the cartoons continued, before the Pope took the opportunity presented by the receiving of Morocco's new ambassador to the Vatican to make clear his views on the subject.
"The Catholic Church," he said, "continues convinced that, to foster peace and understanding between peoples and men, it is necessary and urgent that religions and their symbols be respected."
But he also had a rebuke for Muslims who had risen up in anger over the cartoons.
"Intolerance and violence can never be justified as response to offences, as they are not compatible responses with the sacred principles of religion."
He deplored "the actions of those who deliberately take advantage of the offence caused to religious sentiments to foment violent acts".
In May that same year, however, he called on Christians in western countries "to open their arms and hearts" to Muslim immigrants.
He was addressing the plenary assembly of the Pontifical Council for the Pastoral Care of Migrants and Itinerant People, a convocation of cardinals, bishops, priests and nuns tackling the theme of "migration and mobility from and to countries with a Muslim majority".
The modern dialogue between Muslims and Christians was "important and delicate", the Pope said, and should not concern itself with matters political.
Christians "are called to open their arms and hearts to everyone, whatever their country of origin, leaving the task of formulating appropriate laws for the promotion of healthy existence to the authorities responsible for public life".
Born Joseph Aloisius Ratzinger in the Bavarian village of Marktl on April 16, 1927, the third son of a police officer, he is said to have been inspired by a visit of the Archbishop of Munich to announce, at five years old, that he wanted to become a cardinal.
War slowed his plans. He joined a seminary school but at the age of 14 he was conscripted into the Hitler Youth, drafted into the anti-aircraft corps and, in 1945, found himself facing the advancing allies as an infantryman.
When he was 18, he risked a firing squad by deserting his post. By luck, the German soldiers who intercepted him were not SS but "ones who had had enough of war and did not want to become murderers", he wrote in his memoir, Milestones: Memoirs 1927-1977.
Held by the Americans as a prisoner of war in 1945, he was released after a few weeks and returned to the seminary. He was ordained in 1951 and embarked on an academic career, culminating in his appointment as Archbishop of Munich and Freising in 1977.
The long shadow of paedophilia in the Catholic Church was to hang over his papacy. As a cardinal he had been responsible for the 1962 papal policy Crimen sollicitationis, which many have interpreted as an attempt not to solve, but to cover up institutionalised abuse within the church.
In 2005, shortly after becoming pope, Benedict XVI was forced to seek diplomatic immunity, as head of the state of the Vatican, to avoid liability in a US lawsuit that accused him of conspiring to cover up the abuse of three boys in Texas.
From the outset of his papacy that year, Benedict XVI recognised that the relationship of the Roman Catholic Church with Islam would be one of the central and most sensitive concerns of his tenure as the 265th pope and successor of St Peter the Apostle.
But it wasn't long before the man who had served previously as professor of theology at the University of Regensburg in his native Germany discovered that what might have been acceptable in academic dialogue was very different from what was permissible for the leader of a religion with more than one billion believers.
On September 12, 2006, Pope Benedict returned to the university to deliver a lecture with the seemingly harmless title Faith, Reason and the University - Memories and Reflections.
As part of the speech, he quoted a text, written in the 14th century by one of the last Christian rulers of Constantinople before its fall to the Ottoman Empire: "Show me just what Mohammed brought that was new and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached."
Unsurprisingly, Muslim leaders around the world reacted with disquiet to the remarks, which provoked street protests in Pakistan, India, Turkey and Gaza.
It was, said Ahmed Aboul Gheit, Egypt's foreign minister at the time, "a very unfortunate statement … that shows that there is a lack of understanding of real Islam".
The Organisation of the Islamic Conference expressed its hope that "this sudden campaign does not reflect a new trend for the Vatican policy toward the Islamic religion … and it expects the Vatican to express its real vision of Islam".
Sheikh Yusuf Al Qaradawi, a prominent Egyptian cleric and scholar, called on the Pope "to apologise to the Islamic nation because he has insulted its religion and Prophet, its faith and Sharia without any justification".
Within five days the Pope had done just that, taking to the balcony at his residence at Castel Gandolfo outside Rome.
"I am deeply sorry for the reactions in some countries to a few passages of my address at the University of Regensburg, which were considered offensive to the sensibility of Muslims," he said. "These in fact were a quotation from a medieval text, which do not in any way express my personal thought."
The offence may ultimately have led to better things. In March 2008 the pope announced plans to meet Muslim scholars and religious leaders in Rome, and that November the Catholic-Muslim Forum hosted 24 participants from each religion at a seminar with the theme "Love of God, Love of Neighbour".
"We profess," stated the final declaration of the seminar, "that Catholics and Muslims are called to be instruments of love and harmony among believers, and for humanity as a whole, renouncing any oppression, aggressive violence and terrorism, especially that committed in the name of religion, and upholding the principle of justice for all."
Furthermore, they agreed that "religious minorities are entitled to be respected in their own religious convictions and practices.
"They are also entitled to their own places of worship, and their founding figures and symbols they consider sacred should not be subject to any form of mockery or ridicule."
Among Roman Catholics, the 265th pope will be remembered for many things; but among Muslims perhaps this attempt to bring together in harmony the world's two greatest religions will be recalled as his finest hour.
All eyes will now be on the choice of his successor, who is expected to be elected by the end of March.