Yet he lags far behind Sean Fortune and Brendan Smyth in Irish society's collective consciousness.
Probably because most of the children O'Grady preyed upon were in the US, not here.
"He's the Hannibal Lecter of the clerical world," says attorney Patrick Wall of Manly, McGuire & Stewart in California.
Wall, a former Benedictine monk, has been tracking O'Grady across the globe for several years, serving him with civil actions from his alleged victims in the US.
"He's admitted to abusing post and prepubescent boys and girls. The youngest he molested was a nine-month-old baby and he's slept with mothers to get close to their children."
O'Grady was deported to Ireland in 2000 after spending seven years in prison in the US for sexually abusing two brothers.
The former priest came to public attention when he agreed to feature in a documentary discussing his sexual abuse of children.
Deliver Us From Evil was released in 2006 and featured many of O'Grady's victims discussing the impact his abuse had on their lives.
The film, which was nominated for an Oscar, also showed how high-ranking clergy in California moved O'Grady from one parish to another over several years when allegations of sexual abuse emerged.
In the film, O'Grady attempts to explain the mindset of a paedophile and rapist and it becomes apparent he has no grasp of the devastation his actions have caused. He is childlike and fantastical as he recounts grooming and abusing boys and girls.
Some of the film was shot in a playground in Dublin and outside a school, which caused some controversy.
Scenes where O'Grady's demeanour changes noticeably as children run around him have since been cut from the film. He becomes agitated, uncomfortable and is visibly at a loss as to how to behave.
O'Grady gained the trust of various congregations in northern California in the 1970s and '80s as he was continuously moved around when allegations surfaced. He confessed his problem to Los Angeles bishop Roger Mahoney, but was allowed to continue serving as a priest in various congregations.
In 1998, Mahoney, by then a cardinal, spent four hours on the witness stand in a civil action taken against the diocese over O'Grady's abuse and testified that he sent the Irish cleric to a psychiatrist after the 1984 police investigation into possible molestation.
O'Grady's psychiatrist's report stated: "Father O'Grady reveals a severe defect in maturation, not only in the matter of sex, but more importantly in the matter of social relationships," it stated. "Perhaps Oliver is not truly called to the priesthood."
Despite this, O'Grady was then appointed pastor of St Andrew's Parish in San Andreas and then associate pastor of Sacred Heart Church in Turlock, where his abuse of children continued unabated.
When O'Grady was in prison, having been sentenced for the sexual assault of the two brothers, he struck a deal with the Catholic Church.
He agreed not to testify at the civil action taken by brothers John and James Howard about how he told church authorities about his abuse in return for receiving his full church pension at 65. He turns 65 on 5 June.
In depositions, O'Grady admitted to sexually abusing over 20 children but has only been convicted of abuse against two brothers.
He is listed on the sex offenders' register here, and is required to tell gardaí if he is moving house or country, which he does. Gardaí also monitor O'Grady's movements.
Since his deportation to Ireland in 2000, he has lived in Thurles, Co Tipperary, his native Limerick and various parts of Dublin.
In April 2007, the Sunday Tribune tracked him down to Phibsborough in north Dublin, just 100 yards from a primary school.
He spoke to the Sunday Tribune through his letterbox, saying he would not discuss if he had informed gardaí of his whereabouts.
A neighbour reported O'Grady had been "ogling" her young children in the street.
As required by law, gardaí were informed when he moved from Limerick to Holland almost two years ago.
Gardaí then informed the authorities in Holland.
But detectives here had no idea he was active in a local parish in Rotterdam.SIC: ST