At times controversial, at times reformist, but often conservative - Pope Benedict XVI has made a strong impact with his messages on faith, politics and social injustice.
Here, we take a look at some of the opinions he expressed during his eight-year tenure.
In September 2006, Pope Benedict XVI provoked outrage in the Muslim world with a speech given at the University of Regensburg in Germany.
The lecture, entitled Faith, Reason and the University: Memories and Reflections, explored the historical and philosophical differences between Islam and Christianity, and the relationship between violence and faith.
During his address, Pope Benedict quoted a 14th Century Christian emperor: "Show me just what Muhammad 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."
The pontiff then added that violence was "incompatible with the nature of God and the nature of the soul".
The remarks were interpreted as an attack on Islam and sparked angry protests in Pakistan, India, Turkey and Gaza.
Pope Benedict was forced to issue an apology in response to the angry reactions.
"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.
"These in fact were a quotation from a medieval text, which do not in any way express my personal thought. I hope this serves to appease hearts and to clarify the true meaning of my address, which in its totality was and is an invitation to frank and sincere dialogue, with mutual respect."
ON FAITH AND SECULARISM
Pope Benedict advocated a return to fundamental Catholic values in the face of dwindling follower numbers and the West's increasing secularisation. The day before his nomination, then-Cardinal Ratzinger issued a stern warning about moral relativism and ideological currents that had dogged the church over the past decades.
"The small boat of thought of many Christians has often been tossed about by these waves - thrown from one extreme to the other: from Marxism to liberalism, even to libertinism; from collectivism to radical individualism; from atheism to a vague religious mysticism; from agnosticism to syncretism," he told the Conclave which would elect him the 265th Pope.
"Every day new sects are created and what St. Paul says about human trickery comes true, with cunning which tries to draw people into error. Having a clear faith today is often labelled 'fundamentalism'."
While espousing Christian compassion, he also reaffirmed the "importance of prayer in the face of the activism and the growing secularism of many Christians engaged in charitable work".
"Prayer, as a means of drawing ever new strength from Christ, is concretely and urgently needed," he wrote in December 2005 in his first of three encyclical letters, Deus Caritas Est, or God is Love.
"People who pray are not wasting their time, even though the situation appears desperate and seems to call for action alone... Faith, hope and charity go together."
ON POLITICS AND ECONOMY
In 2009, Pope Benedict called for reform of the United Nations and financial bodies, giving them the "real teeth" needed to tackle economic and social injustice. He made the comments in his third encyclical, Caritas in Veritate, or Charity in Truth. It was his first letter focusing on social issues.
"There is a strongly felt need... for a reform of the United Nations Organisation, and likewise of economic institutions and international finance, so that the concept of the family of nations can acquire real teeth... there is urgent need of a true world political authority," he wrote.
Last December, Pope Benedict also called for a political solution to end fighting in Syria before the country became a "field of ruins".
"I appeal for an end to the bloodshed and easier access for the relief of refugees and the displaced," he said in his annual Christmas message, Urbi et Orbi, in Vatican City.
ON SEXUAL ABUSE
Much of Benedict XVI's papacy was overshadowed by child abuse scandals involving priests. Shortly before his election in 2005, he lamented: "How much filth there is in the Church, and even among those... in the priesthood."
In a pastoral letter to Irish Catholics sent in March 2010, he acknowledged the sense of betrayal in the Church felt by victims and their families. It was the first statement of its kind by the Vatican on the sexual abuse of children.
"You have suffered grievously and I am truly sorry," he wrote. "Your trust has been betrayed and your dignity has been violated... I openly express the shame and remorse that we all feel."
He added that those guilty of abuse must "answer before God and properly constituted tribunals for the sinful and criminal actions they have committed".
He also introduced fast-track rules for defrocking abusive priests and stressed that bishops must report abuse.
ON GAY MARRIAGE
Pope Benedict said the Church considered the distinction between men and women as central to human nature. Deviating from these traditional gender roles was "a violation of the natural order", he said in 2008.
In May last year, he warned of "powerful political and cultural currents seeking to alter the legal definition of marriage". The remarks were made shortly after the US states of Washington and Maryland legalised same-sex marriage.
And, in a pre-Christmas address last December, he denounced gay marriage as destroying the very "essence of the human creature".
"People dispute the idea that they have a nature, given to them by their bodily identity, that serves as a defining element of the human being. They deny their nature and decide that it is not something previously given to them, but that they make it for themselves," he said.
A conservative theologian, Pope Benedict repeatedly warned that contraception was one of a host of trends contributing to a "breakdown in sexual morality".
During his first visit to Africa in 2009, he argued that HIV/Aids was "a tragedy that cannot be overcome by money alone, that cannot be overcome through the distribution of condoms, which can even increase the problem".
But in 2010 the Pope took the world by surprise when he told German Catholic journalist Peter Seewald that the use of condoms could be justified in some exceptional circumstances.
He said condoms could reduce the risk of HIV infection, such as for a male prostitute, in a series of interviews published as a book, entitled Light of the World: The Pope, the Church and the Signs of the Times.
When asked whether the Catholic Church was not opposed in principle to the use of condoms, the Pope replied: "She of course does not regard it as a real or moral solution, but, in this or that case, there can be nonetheless, in the intention of reducing the risk of infection, a first step in a movement toward a different way, a more human way, of living sexuality."