Deirdre, in early Irish literature, the gentle and fair heroine of The Fate of the Sons of Usnech (Oidheadh Chloinne Uisneach), the great love story of the Ulster cycle. First composed in the 8th or 9th century, the story was revised and combined in the 15th century with The Fate of the Children of Tuireann (Oidheadh Chloinne Tuireann) and The Fate of the Children of Lir (Oidheadh Chloinne Lir) into The Three Sorrows of Storytelling (Tri Truaighe Scéalaigheachta). The older version, preserved in The Book of Leinster (c. 1160), is more starkly tragic, less polished, and less romantic than the later version. It describes a Druid’s foretelling, at Deirdre’s birth, that many men would die on her account. Raised in seclusion, she grew to be a woman of astonishing beauty. King Conor (Conchobar mac Nessa) fell in love with her, but Deirdre fell in love with Noísi (Old Irish Noísiu), son of Usnech. They eloped and fled to Scotland with Noísi’s two brothers, where they lived idyllically until they were lured back to Ireland by the treachery of Conor. The sons of Usnech were slain, causing revolt and bloodshed in Ulster. Deirdre took her own life by shattering her head against a rock to avoid falling into the hands of Conor. The later version omits the first half of the story and expands the tragic ending by making Deirdre live for a year with Conor, never smiling, before killing herself.
The story was immensely popular in Ireland and Scotland and survived to the 20th century in Scottish oral tradition; its literary influence continued into the early 20th century, when the Anglo-Irish writers, notably William Butler Yeats and John Millington Synge, dramatized the theme.