King of Ireland 832-845. He fought many battles with the Danes and Norwegians, in most of which although the Danes were worsted, yet the continual supplies pouring unto them made them very formidable; so much so that in this reign they took and fortified Dublin and other strong places upon the sea-coasts. Niall married Gormfhliath, daughter of Donogh, son of Donal.

He is called Niall Caille, for one day when Niall with a large host of cavalry approached the river which is called Callann, and there was a great flood in the river at that time, a youth of the king's party went before them to explore the river and was drowned. The king asked the party to go to his relief and he got no one to go. The king himself went on his horse to relieve him, and as the horse's feet touched the bank of the river, the bank gave way and the river carried away the king, and he was drowned, as it was foretold him that he would die by being drowned at Callann.