It was the first and longest-lasting Norse kingdom in Ireland, founded by Vikings who invaded the territory around Dublin in the 9th century.

The first reference to the Vikings comes from the Annals of Ulster and the first entry for 841 AD reads: "Pagans still on Lough Neagh".

They began to exhibit a great deal of Gaelic and Norse cultural syncretism, and are often referred to as Norse-Gaels.

[citation needed] In 988, Máel Sechnaill mac Domnaill led the initial Gaelic conquest of Dublin.

[citation needed] The extent of the kingdom varied, but in peaceful times it extended roughly as far as Wicklow (Wykinglo) in the south, Glen Ding near Blessington, Leixlip (Lax Hlaup) west of Dublin, and Skerries, Dublin (Skere) to the north.