Britain's most senior Roman Catholic, Cardinal O'Brien, 74, has been no stranger to controversy since he was made a cardinal by the late Pope John Paul II 10 years ago.
In March last year he did not mince his words in suggesting women planning abortions be shown ultrasound scans of their unborn children. "Deeply worrying," was the response of pro-choice group Marie Stopes International.
When the Scottish Government launched a new sex education initiative he described it as "child abuse".
The cardinal was no less strident as one of the most trenchant critics of moves to legalise religious and civil same-sex unions, suggesting gay unions were akin to paedophilia. He asked a group of Scottish politicians in 2006: "What if a man likes little girls – can he adopt a little girl and then just have a little girl at home?"
His outspoken stance led to him being controversially named "bigot of the year" by a gay rights charity last November.
Like many Scottish Catholics, O'Brien has Irish roots. Born in Ballycastle, Co Antrim, in 1938 on St Patrick's Day, he soon moved with his family to Scotland, where his father served with the Royal Navy at Faslane.
He was first ordained as a priest in 1965 and became the Archbishop of St Andrews and Edinburgh 20 years later.
Rising quickly under the mentorship of Pope John Paul II he became only the third Scot since the Reformation to be created a cardinal in 2003.
He stood down from some frontline Church duties last year due to his age and health problems.
However, the cardinal will be part of the conclave that chooses the next Pope.