As plain Joseph Ratzinger he was the Pope's ruthless doctrinal enforcer, described in hushed tones in the Vatican's corridors of power as “God's rottweiler” and “the Panzerkardinal”.

As Pope Benedict XVI he has earned the affection of millions of Catholics with a crowd-pleasing style.It is an extraordinary transformation for a German cardinal who was considered a dogmatic and inflexible hardliner but who can now expect the warmest of welcomes when he makes his first visit to the United States.

Mary Ann Glendon, the new US Ambassador to the Holy See, said that America would find in the Pope a man who had made “a smooth transition from scholar to universal pastor”. She said: “He does not dumb down, and I think that's his particular gift, that he is able to communicate very profound and complex ideas in accessible language.”

The papal makeover owes much to his team of aides. His backroom staff includes Giovanni Maria Vian, the first new editor of L'Osservatore Romano, the Vatican newspaper, for 23 years. Vian was brought in last October to make the paper livelier, up to date, more “global” — and available online. He has opened it up to Protestant and Jewish writers, and has hired its first Muslim journalist.

Vian is part of a new team of progressive papal aides that also includes Mgr Gianfranco Ravasi, the new head of the Pontifical Council for Culture. The key hidden hand, however, is that of Archbishop Claudio Maria Celli, since last June head of the Vatican's Department of Social Communications, which oversees its television and media operations.

Mgr Celli, whose amiable face hides one of the sharpest minds in the Vatican, seized at once on the dangers of the Church being seen as “fundamentalist”. He has at his side an equally sharp-minded Irish priest, Mgr Paul Tighe, brought in as No 2 from Dublin, where he handled PR for the archdiocese.

Their aim, Mgr Tighe says, is to “harness the potential of the media as a means of evangelisation”. Archbishop Celli says that many people in the world have a “deep nostalgia for God” that the Church can meet by being more open and embracing the internet and satellite television.

There has also been a stream of surprising papal initiatives. The Vatican is to host a debate on Darwinism, evolution and intelligent design this year. Pope Benedict has also made overtures to the Muslim world, convening a Catholic-Muslim forum that will hold its first summit in the Vatican in November. The Pope's basic hardline message, nevertheless, remains the need to defend and project the “core values” of Catholicism. During his US visit he has asked to meet Catholic education officials to remind them that they must clamp down on “unorthodox” campus meetings favouring abortion, “planned parenthood” or embryonic stem-cell research.

But according to Cardinal Edward Egan, the Archbishop of New York, the Pope that both America and the world will see is the pontiff who has produced two thoughtful and compassionate encyclicals, on love and on hope, and is about to issue a third, on social problems in an age of globalisation. Benedict will hold the first ever papal Mass at St Patrick's Cathedral and another at Yankee Stadium, as well as visiting Ground Zero, addressing the UN and meeting President Bush.