Born and brought up in England, then associated with Charlemagne's court as a scholar and educator, Alcuin of York displays in letters and poetry a famously apocalyptic reaction to early Viking raids -- specifically the one at Lindisfarne in 793: "... your tragic sufferings daily bring me sorrow, since the pagans have desecrated God's sanctuary, shed the blood of saints around the altar, laid waste the house of our hope and trampled the bodies of the saints like dung in the street." (Letter 20 to Higbald, tr. Allot)
Alcuin also makes reference to a failed missionary attempt in Denmark in the early 8th century in his Life of Willibrord 9; the king Ongendus, described as "more savage than any wild beast and harder than stone," proved unreceptive, but some children were brought back to Francia and baptized. The hostile pagan Frisian leader, Radbod, encountered by Willibrord in the context of his missionary activities figures also in Willibald's Life of Boniface 4-5, but Boniface's further activities then turn to inland Germany rather than to the North.