Cormac son of Art, often viewed as the archetypal king of Tara, is conventionally associated with the Connachta/Uí Néill dynasties. Though there are strong arguments in favour of linking Cormac (sometimes dubbed Ulfota, ‘longbeard’) to an earlier tradition of Tara, by the time the genealogies were compiled in the eighth century he had been integrated into the Connachta schema, with his father Art Óenfer represented as a son of Conn Cétchathach (qv). Accordingly, Cormac was claimed as an ancestor by the later Uí Néill rulers. However, the tale ‘Esnada Tige Buchet’, in which Cormac begets his son Cairpre Lifechair (qv) upon Eithne Thóebfhota daughter of Cathaír Már (qv), may be interpreted as a union with an alter ego of the Leinster goddess Medb – reflecting, therefore, a transfer of the Tara kingship to the Uí Néill dynasties. He is assigned three other sons: Dáire, Cellach, and Muiredach.
The historicity of Cormac is doubtful, though some claim that memories of an early historical ruler (possibly a Laigin or Érainn king) may underlie his legend. Nonetheless, it seems clear that Cormac, as the central character of a group of tales in the Cycle of the Kings, is essentially a literary creation. Included in the regnal poem ‘Baile Chuinn’ and in Middle Irish king-lists, Cormac is accorded a reign of forty years. He is said to have succeeded Mac-Con in the kingship after the latter had given an unjust judgement; one tale implicates him in the assassination of his predecessor. As king, he supposedly secured many victories over the Ulaid and the Laigin, and levied the bóruma (cattle-tribute) on Leinster. According to the tale ‘Cath Crinna’, he defeated the Ulaid with support from Tadc son of Cian, reputedly a nephew of Éogan Már (qv), and granted him lands in Brega (north Co. Dublin and eastern Meath), which explains the presence of the Cianachta in the midlands.
It is said that Cormac's reign ended in abdication, his physical perfection spoiled by the loss of an eye. Other stories, notably ‘Scél na Fír Flatha’, endow him with exceptional wisdom and justice, representing him, in effect, as the Numa Pompilius of Irish law.