Cuchulain, the hero of many Irish legends, is often thought to have been the nephew of King Conchubar mac Nessa, said to have ruled in Ireland in the first century A.D. and himself the hero of a whole cycle of legends. Cuchulain came to the court of Conchubar at the age of six and from that time on he distinguished himself by great deeds of strength. While still very young, he killed the fierce watchdog of the smith Culann and acted as guard in its stead. It was from this that he received his name, Cu Chulainn, "the Hound of Cullan." 

When Cuchulain grew up, he was brave and handsome and daring and many were the stories told of his mighty prowess. 

From Hero Tales from Many Lands