Ragnall Guthfrithson (Old Norse: Røgnvaldr Guðrøðsson; Old Irish: Ragnall mac Gofraid) was a Viking leader who ruled Viking Northumbria in the 10th century. He was the son of Gofraid ua Ímair and great-grandson of Ímar, making him one of the Uí Ímair. He ruled Northumbria in 943 and 944, either with, or in opposition to, Olaf Cuaran. Ragnall and Olaf were driven out of Northumbria by the English in 944. His later life is unknown but it is possible he was the "king of the Danes" who is reported as being killed by the Saxons at York in 944 or 945.