When the Vikings conquered a place, they ‘Vikingised’ the name. For example, they changed Eoforwic to Jorvik, which was easier for Vikings to say. (After Viking times this name was shortened again to simply ‘York’.)
York was founded as the Roman legionary fortress of Eboracum. Then the Anglo-Saxons used it and called it Eoforwic. It was first captured in November 866 by Ivar the Boneless, leading a large army of Danish Vikings.
Eventually, the Vikings were converted to Christianity. The Viking king Guthred was buried in York Minster. York was the most important place in Viking England. All the Viking coinage was minted at York
The Viking kingdom was made part of England in 954. The title King of Jorvik was replaced by the title Earl of York, created in 960. By 1000, the city was the second most important place in England after London.
The Earldom of York was abolished by King Henry II. The title Duke of York was created in 1341. The title of Duke of York has usually been given to the second son of the King or Queen.