BBCPope Francis refused to heed advice to slow down in his final few years, preferring to "die with his boots on", according to a close aide.
In an exclusive interview with the BBC, Archbishop Paul Gallagher, the Vatican's foreign minister since 2014, said the Pope was driven to carry on because he knew he had an opportunity to help the powerless.
While he describes a polite, gentle and compassionate man, Archbishop Gallagher also said Pope Francis knew his own mind and often defied the advice of those around him.
"One thing I always admired about him – though did not always agree with at first – was that he didn't run away from difficult things," said Archbishop Gallagher.
"He would face up to the issues and that showed remarkable courage," he added.
Pope Francis, the first ever Latin American pope, died on Monday aged 88, following a period of ill health that led to him spending five weeks in hospital with double pneumonia.
Sitting in his reception room in the Vatican, Archbishop Gallagher said even he had been stunned by the magnitude of the void he feels has been left by the Pope's death.
"He was very much the voice of the voiceless and was very aware that the vast majority of people are powerless and do not have their destiny in their hands. I think he felt that he could contribute something to make things a little bit better for them," he added.
The Vatican official, who accompanied the Pope on his foreign trips, said he was drawn in particular to the plight of migrants and of women and children caught up in conflict, saying he felt their suffering "in a very real way".
Archbishop Gallagher suggested Pope Francis's sense he could have a hand in helping alleviate suffering is what drove him to keep working at full pace even when told not to, saying he thought it had been "66 or 67 years" since the Pope had taken a holiday.
Pope Francis's very first trip outside Rome was to meet migrants on the Italian island of Lampedusa. But he then travelled extensively abroad visiting more than 60 countries, and not always ones his aides wanted him to go to.
Archbishop Gallagher remembered the time the Pope wanted to visit the Central African Republic and a meeting at which many advisers told him it was too dangerous to go.
"He just said 'well I'm going and if nobody wants to come, fine, I'll go on my own', which of course was rather putting us to shame," said Archbishop Gallagher.
Pope Francis visited the Central African Republic in 2015 as he had wanted to.
"He was always willing to surprise us with who he was willing to meet and talk to. Sometimes this institution [the Vatican] would say one should be a bit more prudent and he wouldn't listen to that."
The Vatican foreign minister described the Pope's ability to scythe through difficult subjects with clarity, reminding officials, for example, to remember migrants as human beings and not just "numbers" in their discussions about them.
On foreign trips over the years, Pope Francis could sometimes be seen nodding to sleep during formal events with politicians and heads of state, or wearing an expression that suggested he was not enjoying the moment.
Archbishop Gallagher acknowledged what observers had long suspected, that the Pope would rather be surrounded by regular people, and particularly young people, rather than meet the "great and the good".
He feels the legacy of Pope Francis has many dimensions but certainly includes breaking down barriers between the public and the institution of the Church and particularly its leader, who he described as "very approachable, very normal".
"I used to like telling anecdotes and he also liked that sort of thing. The last thing he ever said to me, two weeks ago, was, 'don't lose your sense of humour'."
The Vatican said more than 250,000 people paid their respects to Pope Francis between Wednesday and Friday during his lying-in-state in St Peter's Basilica, ahead of his funeral on Saturday.
