Cormac Cond Longas was the eldest son of Conchobar mac Nessa

Conchobar mac Nessa

Conchobar mac Nessa was the king of Ulster in the Ulster Cycle of Irish mythology. He ruled from Emain Macha .-Birth:...

 by his own mother, Ness

Ness (Irish mythology)

Ness , also called Nessa, is a princess of the Ulaid and the mother of Conchobar mac Nessa in the Ulster Cycle of Irish mythology. Her father is Eochaid Sálbuide, king of the Ulaid....

, in the Ulster Cycle

Ulster Cycle

The Ulster Cycle , formerly known as the Red Branch Cycle, one of the four great cycles of Irish mythology, is a body of medieval Irish heroic legends and sagas of the traditional heroes of the Ulaid in what is now eastern Ulster and northern Leinster, particularly counties Armagh, Down and...

 of Irish mythology

Irish mythology

The mythology of pre-Christian Ireland did not entirely survive the conversion to Christianity, but much of it was preserved, shorn of its religious meanings, in medieval Irish literature, which represents the most extensive and best preserved of all the branch and the Historical Cycle. There are...

. His foster father was Fergus mac Róich

Fergus mac Róich

Fergus mac Róich is a character of the Ulster Cycle of Irish mythology...

.

Cormac followed Fergus into exile in Connacht

Connacht

Connacht , formerly anglicised as Connaught, is one of the Provinces of Ireland situated in the west of Ireland. In Ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for...

 after the Deirdre

Deirdre

Deirdre or Derdriu is the foremost tragic heroine in Irish mythology and probably its best-known figure in modern times. She is often called "Deirdre of the Sorrows." Her story is part of the Ulster Cycle, the best-known stories of pre-Christian Ireland.-Legendary Biography:Deirdre was the...

 affair, and fought for Ailill

Ailill mac Máta

Ailill mac Máta is the king of the Connachta and the husband of queen Medb in the Ulster Cycle of Irish mythology. He rules from Cruachan .-Family background, marriage and offspring:...

 and Medb

Medb

Medb – Middle Irish: Meḋḃ, Meaḋḃ; early modern Irish: Meadhbh ; reformed modern Irish Méabh, Medbh; sometimes Anglicised Maeve, Maev or Maive – is queen of Connacht in the Ulster Cycle of Irish mythology...

 against his father in the Táin Bó Cuailnge

Táin Bó Cúailnge

is a legendary tale from early Irish literature, often considered an epic, although it is written primarily in prose rather than verse. It tells of a war against Ulster by the Connacht queen Medb and her husband Ailill, who intend to steal the stud bull Donn Cuailnge, opposed only by the teenage...

(Cattle Raid of Cooley). During the battle he prevented Fergus from killing Conchobar.

When Conchobar died the Ulstermen

Ulaid

The Ulaid or Ulaidh were a people of early Ireland who gave their name to the modern province of Ulster...

 asked Cormac to return to Ulster as their king. However on his journey home he was forced to break his geasa (taboos) and was killed when the hostel he and his men were staying in was raided.