Ivar the Boneless; the Dark Age Rommel!

In AD 851, an Arab merchant visited Tang dynasty China, admired the quality of the porcelain, relished its delicate transparency… but enough about civilized folk!
In the same year, in the hairy, sweaty West, Ivar the Boneless sailed in from nowhere with a posse of Viking longships and seized Dublin with the usual mayhem and slaughter.
He didn’t take it from the Irish, because it was founded by Vikings as a base for slaving and trading (usually the same thing). He didn’t take it from the Vikings who founded Dublin, because a previous wave of Vikings had taken it from them.
So Ivar the Boneless claim-jumped the claim jumpers and with his brother Olaf the White settled in to ruling a town that was basically Mos Eisley but with more Thor worship (they had a very nice grove outside the walls) and fewer aliens (unless you count foreign merchants).
“Settling in” meant stomping on everybody else within reach, teaming up with one clan of Irish kings (there were lots of them) to war on an ungodly alliance of established Irish Kings and Viking settlers. The Death Star moment came after fifteen years of war in AD 866, when Ivar’s forces stormed Clonard Monastery. Olaf the White drowned King Conchobar in a handy font and peace broke out.
What happened next makes Ivar the Boneless look like a slow-motion Field Marshal Rommel.