O'Cahan (Irish: Ó Catháin) is the name of a significant clan in Ulster, a province of Ireland. It has been angiclized to O'Kane and Kane. They are descended from Eógan, son of Niall of the Nine Hostages. In the late Middle Ages, they were the primary sept under the O'Neill Clan of Ulster, holding the privilege of inaugurating the Chief of the O'Neill by tossing a shoe over the new Chief's head in acceptance of his rule. They were Barons of Keenacht and Coleraine in Ulster under the O'Neill, ruling from Dungiven Castle in Limavady.
There is much historical evidence of the clan's ancient Ulster roots. These include Dungiven Priory which is reputed to be the tomb of Cooey-na-Gal O'Cahan, who died in 1385. 'Cooey-na-Gal' means "Terror of the Stranger", so the fact that he is lying here rather than stalking the valley is a great relief to the average tourist.
Turlough O'Cahan owned Dunseverick castle in medieval times, after participating in the First Crusade. Dunseverick was a 'key' ancient site in Ireland and one of the royal roads from Tara, seat of the Kings of Ireland, ended here.
Rory Dall O'Cahan, an Irish harpist of the 17th century, may have penned the popular Irish tune "The Derry Air" or, "Londonderry Air", in order to lament the destruction of the O' Cahan Clan. Consequently, it may have been originally called "O'Cahan's Lament". The tune is best known as the accompaniment to the song "Danny Boy".
The O'Cahan Clan's long battle with the English crown ended in the early 1600s. With that defeat, its lands were contributed to the Derry plantation, during the Plantation of Ulster, as the County Coleraine, and now form the bulk of today's County Londonderry. After the Flight of the Earls in 1607, Sir Donnell Ballagh O'Cahan, Chief of the O'Cahan (and at one time knighted by the English Crown), was captured and sent to the Tower of London, where he died in 1626. There has been no Chief since.