Lorcán Ua Tuathail, known in English as Laurence O'Toole and in French as Laurent d'Eu (1128 – 14 November 1180), was Archbishop of Dublin at the time of the Norman invasion of Ireland.

Lorcán played a prominent role in the Irish Church Reform Movement of the 12th century and mediated between the parties during and after the invasion.

[3][4] The Uí Tuathail (O'Toole) take their surname from their ancestor Tuathal mac Augaire, King of Leinster, who died in 958.

[4] However, at one point Muirchertach's loyalty to Diarmait must have become suspect as Lorcán was imprisoned for some two years in extreme austerity and barely given enough to live on.

Due to the intercession of the abbot of Glendalough – members of Lorcán's family had been buried at one of its churches for generations – relations were amicably restored between Diarmait and Muirchertach.

[1] He was the first Gael to be appointed to the See of a Hiberno-Norse city state; but it is notable that his nomination was backed not only by the High King Ruaidrí Ua Conchobair (Rory O'Connor), King Diarmait Mac Murchada (who had by then been married to Lorcán's sister, Mór); and the monastic community at Glendalough, but also by the Hiberno-Norse clergy and laity of Dublin itself.

To assist in the spiritual formation of the priests and people of the Diocese Lorcán invited the Augustinian Order to become part of the Cathedral Chapter of the Holy Trinity.

Dublin was a walled city, but the Hiberno-Norse citizens were terrified by the Norman knights and men-at-arms, as well as the stories that were being told of their brutality.

To seal the alliance, Diarmait offered his daughter, Aoife Ruadh – who was also Lorcán's niece – in a dynastic marriage to the leader of the Normans, Strongbow.

He had been in negotiations with Diarmait when he and his allies laid siege to Dublin after a band of Norman knights seized the town.

He acted again as mediator when Ascall mac Ragnaill, the last King of Dublin, returned with an army from the Isle of Man and the Hebrides and fought in vain to recapture his kingdom and again when Ua Conchobair laid siege.

[6] The arrival of Henry II of England as Lord of Ireland in Dublin on 11 November 1171 served a number of purposes: first, to rein in his erstwhile Norman subjects before they established a rival Norman kingdom of their own; second, to receive the submission of the Irish kings and princes; third, to arrange a synod at Cashel.

Each Lent he returned to Glendalough to make a forty days' retreat in St. Kevin's Cave on a precipice of Lugduff Mountain over the Upper Lake.

After a stay at the Monastery of Abingdon south of Oxford – necessitated by a closure of the ports – he landed at Le Tréport, Normandy, at a cove named after him, Saint-Laurent.

[8] Due to the claimed great number of miracles that rapidly occurred either at his tomb or through his intercession, Lorcán was canonised by Pope Honorius III only 45 years after his death.

[9] Early devotees of Lorcán compared him with his martyred contemporary Thomas Becket, as a man who had suffered physical attacks for defending both his people from oppression and the independence of the Church from being lost to control by the State, and who had similarly held out the threats of divine curse and excommunication against the oppressors of both.

The bones were supposedly interred at the parish church of Chorley in England, now named St. Laurence's, until they disappeared in the English Reformation.

The reliquary was stolen in 2012, with the Dean of Christ Church saying "It has no economic value, but it is a priceless treasure that links our present foundation with its founding father".

[13] At a special evensong ceremony in Christ Church on 26 April 2018, archbishop Michael Jackson received the heart from a senior Garda.