Final answer:
King Brian Boru led the Irish to victory against the Vikings at the Battle of Clontarf in 1014, where he was killed. The Vikings had a history of raids across Europe and had settled in various parts, including Ireland.
Step-by-step explanation:
At the Battle of Clontarf in 1014, King Brian Boru led the Irish to victory against Vikings, but he died in the battle. This notable event took place long before the Normans invaded England in 1066 and well after the final departure of the Romans from Britain around 400 CE. The Vikings were known for their raids across Europe, often targeting monasteries for their riches, and their presence in Ireland was part of their wider settlement patterns across the British Isles and beyond.