Killeen is the brother of Gerard, and is a giant of well over two meters.
He comes from the Island, a country mentioned by Tenysson. He plays a minor role in the Kings of Clonmel as a bodyguard of the evil outsider, Tennyson.
In the end of the story, he fights Horace in single combat, using a mace and chain. He is killed by Horace during the battle when, after getting his weapon stuck in Horace's broken shield, he is swiftly beheaded by the quick young knight.