Cúchulain, pronounced "koo-hull-in," is an Irish warrior and brother of Max McDaniels. He is known as the Hound of Ulster. His father was Lugh, the sun diety. Cúchulain originally called himself Setanta, but later took the name Cúchulain. It meant the Hound of Culann. He gained this name as a child after he killed Culann the blacksmith's fierce guard-dog in self-defense, and offered to take its place until a replacement could be reared.

At the age of seventeen, he defended Ulster single-handedly in the epic Cattle Raid of Cooley. The queen of Connacht's husband had a magical white-horned bull named Finnenbach. Ulster had its rival, the Brown Bull of Cooley, but would not give it to her. She devised to take the bull by force. Ulster's men were weak and bedridden due to a curse. Because Cúchulain was not born in Ulster, he was not weak. When the queen's men tried to raid Ulster, Cúchulain defeated her army while they were sleeping and left nothing but their heads. The death goddess, Morrigan, even watched him from afar.

The queen eventually made a deal with Cúchulain. She would send a champion to fight him each day. While he was fighting the champions, the queen's men were allowed to march. If Cúchulain defeated the champion, the queen's men had to stop and camp. The queen eventually sent a kinsmen of Cúchulain who served Connacht. The kinsmen preyed upon Cúchulain's loyalty and convinced him to give way to the queen's army. Relunctantly, Cúchulain agreed and allowed the queen and her men to steal the Brown Bull of Cooley. The white bull and brown bull fought each other so devastatingly that it destroyed the surrounding land, and they were never seen again.

It was prophesied that his great deeds would give him everlasting fame, but that his life would be a short one. He is known for his terrifying battle frenzy in which he becomes an unrecognizable monster who knows neither friend nor foe. His main weapon is the Gae Bolga, a spear with a bone shaft and tip which appears to be black metal, but is actually three hairs from the goddess of war forged together.

While Max was reading about Cúchulain, he saw an illustration of Cúchulain entitled "The Death of Cúchulain."