The king of cats widely known in Irish written and oral tradition. He is said to have been as large as an ox and living in a cave at Knowth on the Boyne. In one story, Senchán Torpéist, the chief bard of Ireland, was disgusted when he saw mice walking upon the banquet table and stuck their whiskers in the food he was about to eat. This inspired him compose a satire in which he derided the Irish cats for failing to keep Ireland free of mice. When Írusán, who had incredibly acute hearing, heard the poet recite the satire, he rushed across the land and grabbed him. When they passed the abbey of Clonmacnoise in County Offaly, St. Ciarán intervened and saved the poet by throwing a red-hot poker at the huge cat, who dropped the poet and disappeared.
- Ellis, Peter Berresford. (1992). Dictionary of Celtic Mythology. Santa Barbara: ABC-CLIO, Inc.
- MacKillop, James. (2004). Dictionary of Celtic Mythology. New York: Oxford University Press, Inc.