The Vikings have always pillaged and completed raids everywhere they went, soon years after the Great Heathen Army invaded Northumbria and Wessex, new settlements around the country began to be built. However, most of the other Vikings stayed in their home countries in the North, and still come to raid and pillage kingdoms of England, Ireland, Scotland and recently Wales. The Vikings and the kings of the different kingdoms made a treaty of sorts which is to say the kings have to pay the Vikings to protect their kingdom and people. This way it would ensure peace or so they would hope, if they were not able to pay then the Vikings would take what they wanted from their kingdom. During the late 800's the king of Norway sent multiple raiding parties to Wales as they have extra resources as well as gold and silver then England has.
The most recent raid that was sent to Wales, was in 890AD Torsten Bergenson led the raid and even the battle against the Welsh during the Battle of Anglesey. King Torvald of Gywynedd led the assault against these Northmen or Heathens as they are usually called. Nothing would stop them from battling nor killing each other, however in the end King Torvald had aid from King Aethelwuld of Powys and they were able to come out victorious causing only a couple Vikings alive and set free in hopes they would tell King Harald Fairhair of Norway and finally put a stop to the raids once and for all. However, what these kings did not expect was for Harald not to heed their warnings, instead he continued the raids and made sure that his army was larger than Torvald and Aethelwuld's. Leading the raids would be Torsten's son Ulf Torstenson and he wanted revenge for his father, their fight was not fair, and they were outnumbered by far. Ulf soon became known as Ulf the Merciless due to the way he fights in battle and handles prisoners, everyone says he has a heart of stone and he liked it that way.