At the age of seventeen he defended Ulster single-handedly against the armies of Queen Medb of Connacht in the famous Táin Bó Cúailnge ("Cattle Raid of Cooley").

Lady Gregory retold many of the legends of Cú Chulainn in her 1902 book Cuchulain of Muirthemne, which paraphrased the originals but also romanticized some of the tales and omitted most of the more violent content.

The next morning, the Ulstermen find themselves at the Brug na Bóinde (the Neolithic mound at Newgrange)—the house and its occupants have disappeared, but the child and the colts remain.

Her pregnancy turns into a scandal as she is betrothed to Sualtam mac Róich, and the Ulstermen suspect Conchobar of being the father, so she aborts the child and goes to her husband's bed "virgin-whole".

[11] The nobles of Ulster argue over which of them is to be his foster father, until the wise Morann decides he should be fostered by several of them: Conchobar himself; Sencha mac Ailella, who will teach him judgement and eloquent speech; the wealthy Blaí Briugu, who will protect and provide for him; the noble warrior Fergus mac Róich, who will care for him and teach him to protect the weak; the poet Amergin, who will educate him, and his wife Findchóem, who will nurse him.

He is brought up in the house of Amergin and Findchóem on Muirthemne Plain in modern County Louth (at the time part of Ulster), alongside their son Conall Cernach.

When Sétanta arrives, the enormous hound attacks him, but he kills it in self defence, in one version by smashing it against a standing stone, and in another by driving a sliotar (hurling ball) down its throat with his hurley.

He suggests that Cú Chulainn should train in arms with the renowned warrior-woman Scáthach in the land of Alba (Scotland), hoping the ordeal will be too much for him and he will be killed.

[23] Scáthach teaches Cú Chulainn all the arts of war, including the use of the Gáe Bulg, a terrible barbed spear, thrown with the foot, that has to be cut out of its victim.

[25] Leaving Aífe pregnant, Cú Chulainn returns from Scotland fully trained, but Forgall still refuses to let him marry Emer.

Connla's last words to his father as he dies are that they would have "carried the flag of Ulster to the gates of Rome and beyond", leaving Cú Chulainn grief-stricken.

[26] The story of Cú Chulainn and Connla shows a striking similarity to the legend of Persian hero Rostam who also kills his son Sohrab.

Rostam and Cú Chulainn share several other characteristics, including killing a ferocious beast at a very young age, their near invincibility in battle, and the manner of their deaths.

Lugaid goes on to become High King of Ireland, but the Lia Fáil (stone of destiny) fails to cry out when he stands on it, so Cú Chulainn splits it in two with his sword.

Queen Medb of Connacht mounted the invasion to steal the stud bull Donn Cúailnge, Cú Chulainn allows her to take Ulster by surprise because he was with a woman when he should have been watching the border.

The men of Ulster were disabled by a curse that caused them to suffer from labour pains, so it becomes Cú Chulainn's job to stop Medb's army from advancing further.

When Cú Chulainn wakes up and sees that the boy-troop of Emain Macha have attacked the Connacht army and been slaughtered, he has his most spectacular ríastrad yet: The first warp-spasm seized Cúchulainn, and made him into a monstrous thing, hideous and shapeless, unheard of.

Finally, he fights a gruelling three-day duel with his best friend and foster brother, Ferdiad, at a ford that was named Áth Fhir Diadh (Ardee, County Louth) after him.

[31][32][33] The troublemaker Bricriu once incites three heroes, Cú Chulainn, Conall Cernach and Lóegaire Búadach, to compete for the champion's portion at his feast.

[36] Cú Roí, again in disguise, joins the Ulstermen on a raid on Inis Fer Falga (probably the Isle of Man), in return for his choice of the spoils.

Like other heroes such as the Biblical Samson, Duryodhana in the Mahabharata and the Welsh Llew Llaw Gyffes, Cú Roí can only be killed in certain contrived circumstances, which vary in different versions of the story.

He is often described as dark: in The Wooing of Emer and Bricriu's Feast he is "a dark, sad man, comeliest of the men of Erin",[42] in The Intoxication of the Ulstermen he is a "little, black-browed man",[43] and in The Phantom Chariot of Cú Chulainn "[h]is hair was thick and black, and smooth as though a cow had licked it... in his head his eyes gleamed swift and grey";[44] yet the prophetess Fedelm in the Táin Bó Cúailnge describes him as blond.

Each foot had seven toes and each hand seven fingers, the nails with the grip of a hawk's claw or a gryphon's clench.The Siabur-Charpat Con Culaind (or "Demonic Chariot of Cu Chulaind") tells the story of when Saint Patrick was trying to convert King Lóegaire to Christianity.

[58] A bronze sculpture of the dying Cú Chulainn by Oliver Sheppard stands in the Dublin General Post Office (GPO) in commemoration of the Easter Rising of 1916.

[59] Éamon de Valera unveiled the statue in 1935 as President of the Executive Council (Prime Minister) and described Sheppard's work as "symbolising the dauntless courage and abiding constancy of our people".

[62] An example is the mural painted in 1996 on Lenadoon Avenue, Belfast commemorating Provisional IRA members from the area, which shows Cú Chulainn in the centre.

This is based on Ian Adamson's widely rejected theory that Cú Chulainn was a Cruthin hero and that they were a non-Celtic people who were at war with the Gaels.

[65] A statue of Cú Chulainn carrying the body of Fer Diad stands in Ardee, County Louth, traditionally the site of their combat in the Táin Bó Cúailnge.

[67] Augusta, Lady Gregory retold many of the legends of Cú Chulainn in her 1902 book Cuchulain of Muirthemne, which paraphrased the originals but also romanticized some of the tales and omitted most of the more violent content.

Sheppard's statue of Cú Chulainn is depicted in Samuel Beckett's 1938 novel Murphy as a vice to mock the Irish Free State and the attitude of its inhabitants.