Culann, the smith, who in this capacity may be compared with Hephœstus, or Vulcan lived on the Isle of Man before relocating to Ulster. Culann was also a Divine and Prophet. On the Isle of Man, he manufactured sword, spear, and shield of such transcendent excellence for Conchobar.
Conchobar, who had not yet become King of Ulster, but was an ambitious young man seeking to gain a kingdom. He consulted the famous oracle at Clogher as to how he might best attain his end. The oracle advised him to proceed to the Isle of Man and get Culann to make weapons for him. Conchobar did so, and prevailed on Culann to begin his task; but, while awaiting its completion, he sauntered one morning along the shore, and in the course of his walk met with a mermaid fast asleep on the beach. He promptly bound the syren, but she, on waking and perceiving what had happened, besought him to liberate her; and to induce him to yield to her petition, she informed him that she was Teeval, the Princess of the Ocean; and promised that if he caused Culann to form her representation on the shield surrounded with this inscription, ‘Teeval, Princess of the Ocean,’ it would possess such extraordinary powers that when ever he was about engaging his enemy in battle, and looked upon her figure on the shield, read the legend, and invoked her name, his enemies would diminish in strength, while he and his people would acquire a proportionate increase in theirs. Conchobar had the shield made according to the advice of Teeval, and, on his return to Ireland, such extraordinary success attended his arms, that he won the kingdom of Ulster.
For his art, Conchobar offered Culann to settle on the plain of Murthemne, which was fabled to have been formerly situated beneath the sea.
Once, in Murthemne, he invited Conchobar , by this time king of Ulster, and his retinue to a feast at his house. On the way, Conchobar saw his young nephew Sétanta playing hurling, and was so impressed he invited the boy to join him at the feast. Sétanta told him he would catch him up once the game was over.
The feast got underway, and Culann asked Conchobar if he was expecting anyone else. Conchobar, who had forgotten about Sétanta, answered no, and Culann unleashed his watchdog. When Sétanta arrived he was forced to kill the dog in self defence, and out of obligation offered to take its place until a replacement could be reared. For this he was renamed Cú Chulainn – “Culann’s hound”.