The remarkable life of John Paul II has reached another milestone. His papacy has become the third-longest in the history of the Catholic Church.
On Sunday, the Polish-born pontiff celebrates 9,281 days in office. Over the past 2,000 years, only two men have served longer.
The pope has seen many changes during his papacy
The first - in every sense - was St Peter, the apostle chosen by Jesus to lead the church after his death.
The exact dates are unknown, but he is believed to have been in charge for somewhere between 34 and 37 years.
Among the popes who followed in his footsteps, the record is held by Pius IX, who was elected in 1846 and reigned for 31 years.
When the little-known Karol Wojtyla was elected in 1978, few imagined his papacy would be so long or so extraordinary.
The Vatican, which meticulously compiles papal statistics, records that he has now created 476 saints - more than all the other popes put together.
During his papacy he has made 102 overseas journeys, visiting a total of 129 countries. And 17 million people from all over the world have attended papal audiences.
But the man elected pope when he was an energetic 58 is now approaching his 84th birthday, and suffering from Parkinson's disease.
His frail health has raised questions about his ability to continue in the job, although it has been said many times that he has no intention of resigning.
Among those concerned about the possible impact on the church is Eamon Duffy, professor of the history of Christianity at Cambridge University.
Papal Top 10
St Peter (30-64/67AD)
Pius IX (1846-78)
John Paul II (1978- )
Leo XIII (1878-1903)
Pius VI (1775-1799)
Hadrian I (772-795)
Pius VII (1800-1823)
Alexander III (1159-1181)
St Silvester I (314-335)
St Leo I (440-461)
"There are dozens and dozens of popes who have ended their lives rather ill, and there have been a significant number who have ended their lives gaga," he says.
"It hasn't mattered before because they were elderly gentlemen confined to a run-down city on the edge of Europe, with relatively little control over the church.
"So if you've got a pope who loses his marbles, that's bad news for Italy, but it doesn't much matter for anywhere else.
"But it really does matter now, in a system as centralised as the modern Roman Catholic Church, if the pope is not in charge."
Those who work with John Paul II insist that he remains mentally sharp, and the illness affects only his physical condition.
But the pontiff is likely to experience a gradual worsening of his condition, according to Dr Ray Chaudhuri, a consultant neurologist and an expert on Parkinson's disease.
The Pope has suffered from Parkinson's disease for some time
"Although he does look quite tired at times, and the tremor does become visible, the fact that he is still able to function in his public duties says to me that the illness is relatively well controlled," he says.
"But one has to balance that by saying that the condition does progress and ageing does accelerate that progression to some extent."
Dr Chaudhuri says patients with Parkinson's disease may develop problems with memory, sleep and balance. Their symptoms can be aggravated by stress.
In prescribing drugs to control the disease, a fine balance is needed to control the patient's movements without producing too many side effects.
"One unfortunate side effect might be hallucinations, which are often visual," he says.
"There may also be problems with behaviour, and sometimes confusion - people may not be aware of what is happening around them.
"With the Pope's condition being fairly advanced, there is a certain degree of inevitability that some of these side effects will occur."
Professor Duffy says the pope's condition is already a concern, given the administrative demands of the papacy.
"He is an old, tired, sick man," he says.
"I imagine if you put a mound of paperwork in front of him, his attention span in dealing with it will be fairly limited."
Professor Duffy believes there could be problems if bishops around the world are not sure whether the decisions being made at the Vatican have the full approval of the pope.
"Twenty-five years ago, this was a pope who skied and swam, who travelled the world, who was lecturing, preaching and writing endlessly.
"Now, if you attend a papal mass, he is a frail figure who often falls asleep in the course of the ceremony.
"It is deeply moving that this titan is reduced to a trembling old man. It arouses feelings of awe and affection, for his courage and his fidelity.
"But he is more than a ceremonial figure. He is also the chief executive of the largest religious corporation in the world, and in theory, all serious decisions are made by him.
"The organisation that depends on a leader who ought to be dynamic, but is extremely frail, is in trouble."