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.

Irish, also known as Irish Gaelic or simply Gaelic, is a Goidelic language of the Insular Celtic branch of the Celtic language group, which is a part of the Indo-European language family. Irish is indigenous to the island of Ireland and was the population's first language until the 19th century, when English gradually became dominant, particularly in the last decades of the century. Today, Irish is still commonly spoken as a first language in areas of Ireland collectively known as the Gaeltacht, in which only 2% of Ireland's population lived in 2022.