The pontificate of John Paul II was one of the longest in the history of the Catholic Church.
Few popes of any century have had such an impact, either on the Church or the times in which they lived.
He saw himself as the universal pastor, using air travel and the mass media to take his message to the world.
He became a familiar sight - arriving in another foreign land, kissing the ground, and then preaching at an open air mass to perhaps a million people.
Familiar routine: Pope John Paul II kissing the ground, this time in Lithuania
"Through those amazing journeys he showed the Catholic Church to the world as never before," said John Wilkins, former editor of the Catholic magazine, The Tablet.
John Paul II travelled to virtually every corner of the world to meet his flock, re-defining the papacy for a modern age.
Whoever succeeds him will feel obliged to follow his example. Media skills and fluency in several languages are now a requirement for the job.
"John Paul II was a remarkable pope," said Madeleine Bunting, a writer on church affairs.
"For millions of Catholics he really was a father figure, and he used the global media astonishingly astutely. We have never had such a well-known pope, and such a popular pope."
When he was elected in 1978, few outside Poland had heard of Karol Wojtyla, the archbishop of Krakow.
But the cardinals who chose him knew they could count on him to uphold traditional beliefs at a time when the teaching of the Church was being questioned by many Catholics.
And during his papacy, there was no wavering in the Vatican's position on contentious social issues such as birth control, abortion and divorce.
Neither was the celibacy of the priesthood or the role of women in the Church ever up for discussion.
This, too, is part of his legacy. In fact, the uncompromising views of John Paul II may now limit the room his successor has for manoeuvre.
"The next pope is going to have a very difficult time untying things like birth control, abortion and women priests," said Ms Bunting.
"With all of these sensitive issues, John Paul II has made it very, very difficult for his successor, because a pope cannot undo the teachings of his predecessor.
"For example, he was so categorical that women priests were not acceptable that it will take a long time - decades - for that to be changed gradually."
But while John Paul II was a conservative in terms of theology, he was also a pope with a keen interest in social justice, not least in his homeland.
As a young man growing up in Poland, Karol Wojtyla had witnessed the rise of Nazi Germany. Then after World War II, he faced the challenge of being a priest in a Communist state.
Pope John Paul II as a young man in Poland
"When the church elected a Polish pope in the middle of the Cold War, everybody felt it was a real political statement," recalls Father Thomas Reese, an authority on the workings of the Vatican.
"John Paul II played an extremely important role in bringing down Communism in eastern Europe. His election was inspirational."
The pro-active style of John Paul II underlined the fact that a pope is not just a spiritual leader - he is also a player on the world's diplomatic stage.
One theme of his papacy was his attempt to reach out to other faiths, in search of reconciliation after centuries of hostility and suspicion.
He travelled to Islamic countries and became the first pope to set foot in a mosque. As a symbol of religious tolerance, it took on new meaning after the events of 11 September 2001.
But while some in the church are already talking about "John Paul the Great", others are more doubtful about his legacy.
They say that during his reign, the Vatican exercised too much power, and was less likely to tolerate dissent.
They want to see a different kind of papacy, with bishops around the world having a greater say in how the Church is run. That would be a challenge to the authority of the Church's central bureaucracy, the Curia.
With former US President Ronald Reagan
"Many bishops and cardinals felt that at the end of the reign of John Paul II, the Curia got out of hand," said Father Thomas Reese.
"They felt it was imposing its will on the local bishops, and really not being sensitive and listening to their concerns. So I think there is going to be a backlash in the conclave against the Curia."
John Wilkins, former editor of The Tablet, also believes that there could be a change in the relationship between the pope and the church outside Rome.
"It is a curious paradox of a very centralised papacy that in some ways the Church has never been so open in the direction that it follows now," he said.
"John Paul II has laid the foundations for the future. He was the last pope of the 20th Century, rather than the first one of the 21st Century."
But whoever is chosen to succeed him, it will be a tough act to follow.
John Paul II was the second longest-serving pope since the apostle St Peter, who is regarded as the first head of the Catholic Church, but never formally held the title.