Deirdre is a tragic heroine in the Ulster Cycle of Irish mythology. She is also known by the epithet "Deirdre of the Sorrows".

The Ulster Cycle, formerly known as the Red Branch Cycle, is a body of medieval Irish heroic legends and sagas of the Ulaid. It is set far in the past, in what is now eastern Ulster and northern Leinster, particularly counties Armagh, Down and Louth. It focuses on the mythical Ulster king Conchobar mac Nessa and his court at Emain Macha, the hero Cú Chulainn, and their conflict with the Connachta and queen Medb. The longest and most important tale is the epic Táin Bó Cúailnge. The Ulster Cycle is one of the four 'cycles' of Irish mythology and legend, along with the Mythological Cycle, the Fianna Cycle and the Kings' Cycle.