Cumhall (in Irish pronounced as /kuːl̪ˠ/; Irish, Old (to 900);: '''Cumall''') or Cumhall mac Trénmhoir ("son of Trénmór/Tréanmór" meaning "strong-great") is a figure in the Fenian Cycle of Irish mythology, a leader of the fianna and the father of Fionn mac Cumhaill.
The most important text regarding the family of Finn (son of Cumaill) is Fotha Catha Chnucha ("The Cause of the Battle of Cnucha"), as it is contained in the ancient parchment Lebor na hUidre (LU), dated to the 12th century. Otherwise, the next most important tract is the Macgnímartha Finn ("The Boyhood Deeds of Fionn") copied in a 15th-century manuscript.
According to the Fotha Catha Chnucha, Cumhall mac Trénmhoir was son of a petty king, and served the High King Conn Cet-Chathach "of the Hundred Battles". Cumhall was also Conn's half-uncle, his mother being the mother of Conn's father,.
Cumhall became suitor for the hand of Muirne Muncaim "of the fair neck", daughter of the druid Tadg mac Nuadat, but Tadg refused him, so Cumhall forcibly carried away Muirne in elopement.
Tadg, slighted by Cumall's sweeping away his daughter, appealed to Cumall's lord, Conn of the Hundred Battles, and Conn gave choice of either relinquishing the daughter or suffer banishment. Cumall refused to give up his wife, and Conn made war against Cumhall, and Cumhall was killed by Goll mac Morna in this Battle of Cnucha, located at what is today Castleknock.[3] Goll then took over leadership of the Fianna, as explained in the Magnímartha Finn.[4]
Cumhall's wife Muirne was already pregnant with his son, Fionn, and Muirne's furious father Tadg not only refused to accept her back, but ordered her burnt to death.[5] Cumhall's wife however seeks Conn's protection, and in exile she delivers a child which she names Demni. Demni (Demne) later became Finn.[6]
Cumhall is reputed to be buried within the grounds of Castleknock College, supposedly under a hill upon which an old water tower now stands.
Attempts to connect Cumhall with Camulus, a Celtic god of war known from Roman-era inscriptions, are now largely rejected. Old Irish cumal means "female slave", and it is possible that a noble father was invented for Fionn to obscure an ignoble origin. Alternatively, some early texts call the hero "Fionn mac Umaill", which may indicate his father's name was originally Umall.