Connla was born from the relationship between Cú Chulainn and Aife. Aife, attacking the Land of Shadows while Cú Chulainn was training under Aife's sister Scáthach, was defeated by Cú Chulainn in a duel. He then perused her romantically for a time, but he eventually parted from her when leaving the Land of Shadows. He asked her that if she was to bear his child that she name the child Connla and send him to Ulster. Connla was to be tasked with three vows, "To not answer his name when asked," "To not change course," and "To not back down from a fight."
After the war with Connacht, Connla came down to the coast and started fighting the warriors of Ulster. He defeated any warrior who spoke to him, so the king decided that only Cú Chulainn could defeat him. Although Cú Chulainn's wife pleased with him not to go, he was unable to reject a royal order. Cú Chulainn fought him, eventually felling him with Gáe Bolg. As Connla died, he remarked that Scáthach did not teach him that technique.