So I've been posting the BBC shorts about Cu Chulainn. Unfortunately, I haven't been able to locate the next one in the series, which is really one of the more important ones: How Setanta got the name Cu Chulainn.
As we saw, Setanta went to Emain Macha and pleaded with King Conor to let him take his place among the Boy's Troop. Setanta became a favorite of the King. He also became an outstanding Hurling player. (Hurling being an Irish sport similar to field hockey, or lacrosse if you're so inclined.)
One day the King went out to visit his smith, Cullen. Cullen was known for his viscious hound which protected the homestead and smithy. As he went out, the King saw Setanta playing Hurling in the field with the other boys and invited him along. Setanta said he would come visit after the game. The King went on his way to Cullen's hall and was entertained as evening fell.
Suddenly, there was a commotion outide! The King remembered that Setanta was yet to arrive, and then noticed that the doors were bolted shut. Cullen had locked them after he thought all the guests were inside, and then let out his massive hound to patrol the grounds.
The King feared the worst for Setanta...
Ok, so this video subverts the story... Setanta was found outside with the dead dog. He had killed it with his Hurley, the stick used in the game. Some versions have him batting the hard ball down the hound's throat.
The King was overjoyed to see Setanta was still alive. Cullen, on the other hand, was very upset that his unique dog was now dead, and no longer available to protect his possessions. So Setanta offered to come to Cullen's home every night for a year -- the time it would take to train a new guard dog -- and protect the property.
And so Setanta was given the nickname, "The Hound of Cullen" or Cu Chulainn.