When Joseph Ratzinger was elected Pope in 2005, the choice divided Catholics.
Traditionalists cheered the appointment of a man who, as a cardinal, had for two decades ruled the Vatican's doctrinal watchdog with a mitre of iron.
Liberals feared the conclave had made the most divisive choice imaginable. But Pope Benedict XVI turned out to be a pope of surprises - a tradition he maintained with the shock decision to resign.
The surprises began when he issued his first major teaching document. The encyclical's subject - love - was not what was expected from a dogmatic hardliner. From the outset he understood that as Pope he had to make a gear-change to a much more pastoral and inclusive approach.
That shift was evident on his visit to the UK in 2010. Shriller secularists had predicted that the man once known as God's Rottweiler would not be well received because of his uncompromising views on society's rampant materialism and moral relativism.
But there was a gentleness about the way this German shepherd stated his religious certainties which showed a willingness to open up a dialogue with the secular world.
Benedict XVI's most striking quality as Pope has been his thoughtful, cultured, deeply read intellect which has enriched the dialogue with even those who disagree with his religious conservatism.
Early on, he did not understand the impact he might have by such thinking aloud. One of his first public forays was to return to his old university at Regensberg with a lecture on faith and reason which carelessly quoted a medieval attack on Islam.
Remarks which went unnoticed from an academic theologian, he learnt, could cause riots when they came from a Pontiff.
But by the time he spoke to Britain's civic leaders in Westminster Hall there was a humility to his acceptance of the need for dialogue between church and state.
There was a gentle wisdom to Benedict XVI which even attentive sceptics found thought-provoking. The headlines, however, concentrated on sensational issues throughout his eight years in office. The church's opposition to abortion and euthanasia, along with its intransigence on gay relationships, and its refusal to allow the distribution of condoms in Africa, alienated it from secular society. Benedict was immovable on that.
But on the issue of paedophile priests he received a more unfair press. Behind the scenes he cracked down on what he privately described as the filth of priestly abusers.
He pressed his reluctant predecessor, John Paul II, to take a firmer line. He introduced fast-track internal trials, extended abuse investigations and penalised priests guilty of internet offences against children.
But he did all this in private, using canon law rather than reporting offenders to police, compounding the culture of secrecy for which victims criticised the church.
After two conservatives, a more progressive pope? That is unlikely, though we may after centuries of white popes get a black one.
Whoever succeeds, it will be to a papacy which Benedict XVI, through his resignation, has subtly changed. By not dying in office, he has set aside the old idea that the papacy was a vocation unto death. It is now a ministry which can be set aside when appropriate.
The decision to quit may turn out to be the most modernising act he has ever committed.
In the frame
Cardinal Angelo Scola, 71
Archbishop of Milan
Scola is close to Benedict, has a fierce intellect and leads the most important archdiocese in Italy - no small thing given that Italians still dominate the College of Cardinals.
Cardinal Gianfranco Ravasi, 70
Head of the Vatican's culture office
He is another intellectual heavyweight who quotes Hegel and Neitzsche as easily, and almost as frequently, as the Gospels. He has climbed into the spotlight with his "Courtyard of the Gentiles" project, an initiative to enter into dialogue with the worlds of art, culture and science and most importantly atheists.
Cardinal Christoph Schoenborn, 68
Archbishop of Vienna
Benedict's onetime theology student, Schoenborn has long been considered to have the stuff of a pope - multilingual, affable and, most importantly, Benedict's blessing. He has been dealing, however, with difficulties in Vienna, where a revolt of dissident priests has questioned church teachings on everything from women's ordination to celibacy for priests.
Cardinal Peter Kodwo Appiah Turkson, 64
Formerly Archbishop of Cape Coast
The Ghanaian is one of the highest-ranking African cardinals at the Vatican, now heading the Vatican's office for justice and peace. He became a cardinal in 2003.
Cardinal Francis Arinze, 80
Formerly Archbishop of Onitsha
Prefect Emeritus of the Congregation for Divine Worship and the Discipline of the Sacraments. He has been a cardinal since 1985. Like Turkson, the Nigerian has a long history of inter-faith dialogue with Muslims and could help build bridges following Benedict's lacklustre ecumenism.
Cardinal Leonardo Sandri, 69
Prefect of the Congregation for the Oriental Churches
The Italian-Argentine is head of the Vatican's office for Eastern rite churches. Sandri earned fame as the "voice" of Pope John Paul II when the pontiff lost the ability to speak because of his Parkinson's disease.
Cardinal Joao Braz de Aviz, 65
Formerly Archbishop of Brasilia
The Brazilian has earned praise as head of the Vatican's office for religious congregations, even though he's only held the job since 2011. He has had the difficult task of trying to rebuild trust between the Vatican and religious orders.
Oscar Rodriguez Maradiaga, 70
Archbishop of Tegucigalpa
The head of Caritas Internationalis from Honduras is considered by the Church's more traditional members to lean too far left. He was president of the Latin American Episcopal Conference from 1995 to 1999.
Cardinal Odilo Pedro Scherer, 63
Archbishop of Sao Paulo
The German-Brazilian became a cardinal in 2007 and is considered a moderate.
Cardinal Antonio Tagle, 56
Archbishop of Manila
Tagle is a rising star in the church and is very popular in Asia, but at 56 he is considered too young.
Cardinal Marc Oeullet, 68
Formerly Archbishop of Quebec
The Canadian is a contender, earning the respect of his colleagues as head of the Vatican's office for bishops, a tough and important job vetting the world's bishops, and is president of the Pontifical Commission for Latin America.