John de Courcy, of Stoke Courcy, in Somerset, had come came to Ireland around the year 1171 as part of the Norman invading forces, brought in as mercenaries working for Dermot MacMurrough, the ousted King of Leinster, to help him regain his position as King.

John is very ambitious and wants lands for himself.

He had decided to invade the north of Ireland which was controlled by the Irish clans.

He assembles a small army of twenty-two knights and three hundred foot soldiers in early January 1177 and marches north at the rate of thirty miles a day, skirts the back of the Mourne Mountains and takes the town of Dun de Lethglas (later Downpatrick) by surprise.

After two fierce battles in February and June 1177, de Courcy defeats the last King of Ulaid, Ruaidrí Mac Duinn Sléibe.

He has done all this without the permission of his king, Henry II.

After conquering eastern Ulster, he establishes his capital at Carrickfergus, where he builds an impressive stone castle.

He marries Affreca, daughter of Godred II Olafsson, King of Mann.

It is likely that the marriage, as in the case of many kings and those aspiring to be kings during this age, is political, to seal an alliance with her father, who pays homage to the King of Norway.