Cat Head is an antagonist in the folklore story Finn MacCumaill and he is one of six major antagonists of that story. He comes from the far East and seeks to burn a dam built by a king of Ireland.
After escaping from his grandfather and a giant; Finn Macumail arrived at a scene where a group of labourers were building a wooden dam to protect a king's river, but every night it mysteriously burned to the ground. Several of Ireland's champions had vowed to protect the dam, but every night they failed, and they were now under sentence of death. Finn had previously obtained supernatural knowledge by biting his thumb all the way down to the marrow, so he bit his thumb again, and realized that there was an evil witch on the East side of the world and every night she sent her sons to burn the dam. She did this every night having an obssession with destroying this particular dam. So, she sent her youngest son off to do the job. Finn volunteered to protect the dam and was taken to the king who said Finn could have his daughter for saving the dam but if he failed the king would have his life.
The youngest son
Night fell and the youngest son flew to the dam, set torches, and burned it, but Finn's hound Bran pushed them into a river as soon as they landed. The son whined about being defeated and then attacked Finn. But together, Finn and Bran defeated and killed him.
The witch was angry at the delay and sent her second eldest son off to face whoever it was at the dam.
The second son
Finn was ready for the next son, and he fought him, and killed him with Bran's help. He also pushed his torches into the river. This utterly infuriated the witch so she turned in her need to her eldest son, Pus au Chine, aka "Cat Head" who had a human body but a cat's head. She only sent him out in great need. She told him to fly to Ireland and burn the wretched dam and punish his brothers for their lateness.
The eldest son, Cat Head
Pus au Chine flew off to the dam and tried to burn it, but he was defeated by Finn and Bran. This battle proved to be the strongest and most vicious. Bran was able to skin Pus alive, but he kept fighting. Nothing seemed to weaken him, and in fact it was Finn who was weakening. Bran kept biting at Pus but he beat Finn into submisison.
Now, the witch saw what was happening and sped over to the dam herself, and she had a phail of magic liquid which could resurrect her dead sons, and Finn managed to get enough strength to chop off Cat Head's head. But his head lived on, when the body died, and leapt into the air to continue gnawing Finn. Bran couldn't help. The witch arrived, and Finn knew that her liquid could permanently kill Cat Head, so he swept her out of the air, and swept the bottle out of her hand. She shrieked so loud she caused rocks to split and hard grass to go soft. Then she wrestled with Finn for the bottle but he took the liquid and rubbed it round Cat Head, who fell dead. Then he chopped off the witch's head and also killed her.