The name of Cú Chulainn’s son, killed by his own father, was Connla.
Connla was the son of the Ulster hero Cú Chulainn and the Scottish warrior Aífe. Before Cú Chulainn left Aífe, he gave her a gold ring and instructed that their son be sent to Ireland when he was old enough. He also imposed rules, or geasa: Connla was not to turn back, refuse a challenge, or reveal his name.
When Connla arrived, his extraordinary martial skill alarmed the Ulaid. He defeated several champions, but Cú Chulainn eventually confronted him. Connla refused to identify himself, so the two fought. Cú Chulainn used the deadly Gáe Bulg, mortally wounding the boy before recognizing that he was his son.
The tragedy resembles other father-and-son recognition myths, including Rostam and Sohrab in Persian epic. Connla is also called Conlaoch in some retellings, while later literary adaptations sometimes change details such as his mother’s identity.