Pope Benedict XVI has a reputation as a charming and shy man who is also deeply conservative in his outlook and teaching.
Before being elected pope and becoming leader of the world's 1.2billion Catholics he held the post of Prefect of the Congregation for the Doctrine of the Faith. It was there that he gained the nickname "God's Rottweiler" for his pursuit of Catholic theologians and clergy seen to stray from orthodox teaching.
He was hailed a hero by conservative Catholics and viewed with suspicion by liberals.
The German-born Pontiff, 85, who is resigning due to his age and diminishing strength, was elected to the papacy in 2005, only the second non-Italian Pope since 1522 and the oldest on election since the 18th century.
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But Pope Benedict's decision to retire should not come as too much of a surprise.
He said after he was elected to the Papacy that he had prayed not to get the post and was hoping for a peaceful old age.
As the powerful Cardinal Joseph Ratzinger, he was already well-known within the Catholic world before his election to the top job.
His image on elevation to the Papacy was one of an enforcer of Catholic orthodoxy and a cerebral disciplinarian who was unafraid to crack down on liberals and dissidents within the church.
His pronouncements before becoming Pope included labelling homosexuality a "more or less strong tendency ordered toward an intrinsic moral evil" and saying rock music could be a "vehicle of anti-religion".
The Pope has also proved himself to be strongly against the ordination of women as priests, euthanasia, abortion and the use of artificial birth control.
Since his election as Pontiff his image has softened, leading him to be dubbed "Benedict the Benign" in some quarters - but he has also attracted considerable controversy.
The Pope's 2009 visit to Africa was overshadowed by a row sparked by comments he made while flying to the continent in which he rejected condoms in the fight against Aids.
His decision in 2009 to lift the ex-communication on renegade English cleric Richard Williamson, who made comments suggesting only 200,000 to 300,000 Jews died in the Holocaust and none perished in gas chambers, also caused uproar.
The Pope later issued a letter expressing his regret about the damage the affair caused to relations with the Jewish community, saying he had not known about Williamson's stance on the Holocaust when he took the decision to lift the ex-communication.
Perhaps his biggest setback as Pope was during his visit to Germany in 2006 when he was caught in a firestorm of criticism from the Islamic world after giving a lecture at his old university of Regensburg.
Quoting from an obscure Medieval text, he cited the words of a Byzantine emperor who characterised some of the teachings of the Prophet Mohammed, Islam's founder, as "evil and inhuman" - remarks that touched off widespread anger across the Muslim world.
The anger and violence sparked by his comments including attacks on seven churches in the West Bank and Gaza posed one of the biggest international crises involving the Vatican in decades.
In Somalia, gunmen killed an Italian nun and her bodyguard at the entrance of a hospital where she worked, in an attack that some feared was linked to the outrage over the Pope's remarks.
He later apologised, saying he was "deeply sorry" about the angry reaction to his remarks about Islam and holy war, saying the text he quoted did not reflect his personal opinion.
The Pope was made Archbishop of Munich and Freising in 1977 after a career as a university professor.
He was born in the village of Marktl am Inn in Bavaria - he explained on a visit to Germany after his election "my heart beats Bavarian".
His formative years coincided with the lifespan of the Third Reich. His family opposed National Socialism but did not participate in public resistance to the Nazis.
He was forced against his will into Hitler Youth at the age of 14 and into the Wehrmacht at 16, serving in an anti-aircraft unit before deserting towards the end of the war.
He was once viewed as a progressive within the Catholic Church and played a key role in the reforming Vatican II, the meeting between 1963 and 1965 that introduced sweeping reforms to the church.
It is believed that his experience of Marxist unrest amongst students in the theology faculty in Tubingen, southern Germany, in 1968 where he was a professor contributed to his conservative outlook.
In private, the Pope is known to be an accomplished pianist and a lover of Mozart.
He is also a cat lover and, as Cardinal Ratzinger, was known to have looked after stray cats in Rome.