Name the Ard Ri who defeated the Vikings at the Battle of Clontarf in Ireland in 1014?

Answer 1

I had to look that up... Ard Ri apparently means high king.

Anyway, the winner at Clontarf was Brian Boru, who died in the battle, even though his forces won a decisive victory.

Answer 2

BRIAN BORU’S LAST COSTLY VICTORY

The Irish High King wanted to unite his people, but his enemies - including the Viking Brodir of Man - stopped him at Clontarf in 1014.
Brian, though reluctant to take an active part in a battle on Good Friday, did ride before his assembling forces, carrying a crucifix in one hand and a sword in the other. He gave a short but inspiring speech to his warriors assembled to do battle and then retired to the rear, accompanied by a number of personal escorting guards, who formed a shield wall around him. (Brian Boru had camped at what is now Kilmainham the night before, in a dense stand of oak trees known as Tolmar’s Wood.) The Irish, incensed by years of bloody skirmishes, of loved ones being killed or captured and homes destroyed, prepared to destroy the hated Vikings and their renegade Irish allies.

On modern Dublin’s Sandymount Strand, a young boy with fair hair and sea-blue eyes walks alone on the beach. He leaves footprints in the damp sand. Seagulls wheel overhead, crying. The boy is paying no attention to the great modern city of Dublin which rises behind him. Insted he keeps gazing out to sea, watching the waves coming rolling in with their message from foreign shores. He dreams of what lies beyond the horizon. Some day he may go and see for himself.

The Vikings never left Ireland.

They are still there!