Conchobar was an important figure in the Ulster Cycle, appearing in the Táin Bó Cúailnge and a number of other stories where he is depicted as a good king.
In the earliest, Ness, daughter of Eochaid Sálbuide, the then king of Ulster, asks the druid Cathbad what it is an auspicious time for.
Conchobar demands compensation from Eochu for the killing of his father, Fachtna Fáthach, and is granted land, status and the High King's daughter in marriage.
Deichtine is the mother of Cú Chulainn, by either her mortal husband Sualtam or the god Lugh, making Conchobar his uncle.
The child is named Deirdre, and Conchobar decides to have her brought up in seclusion from men, intending to marry her when she comes of age.
Eventually, Conchobar tracks them down to a remote island and sends Fergus to them with his guarantee of safe passage home.
Fergus, outraged by the death of his son and the betrayal of his honour, makes war against Conchobar, alongside Cormac Cond Longas, who sides with his foster-father against his father, and Dubthach Dóeltenga.
Deirdre lives with Conchobar for a year, but during that time she never smiles, rarely eats or sleeps, and refuses to be comforted.
Cú Chulainn fights a series of single combats against Connacht champions, hoping to give the Ulstermen time to recover and take the field.
He wants to make war against Connacht, but it is now winter, so Cathbad advises him to wait until summer when his men and horses will be fresh and energetic, and in the meantime, call on all his foreign allies to bring reinforcements.
When asked where he wants to pitch his tent that night, he selects Ros na Ríg (Rosnaree) on the River Boyne.
The battle goes badly for the Ulaid until Conall Cernach joins the fray because the wavering Ulstermen are too scared of him to retreat.
[15] Conchobar is eventually killed as a result of a wound inflicted by the Connacht warrior Cet mac Mágach.
Cet had stolen one of Ulster's trophies of battle, the petrified brain of Mesgegra, king of Leinster, and shoots it from his sling so it embeds itself in Conchobar's head; this is supposed to have taken place at Baile Ath in Urchair, (Ardnurcher).
[16] Conchobor's physicians are unable to remove it, but sew up the wound and tell the king he will survive so long as he doesn't get excited or over-exert himself.
Seven reasonably peaceful years later, Conchobar is told of the death of Christ and becomes so angry that the brain bursts from his head, and he dies.
[17] While this account of his death has been superficially Christianised, it also bears strong resemblances to the Scandinavian myth of Thor's fight against Hrungnir, suggesting either a common origin of the two episodes or a later borrowing during the era of Viking influence in Ireland.