They had a well known reputation:
Parts of the tactics and warfare of the Vikings were driven by their cultural belief, themselves rooted in Norse culture and
religion, and vividly recalled in the later
Icelandic sagas. In the early Viking Age, during the late 8th century and most of the 9th, Vikings consisted of smaller tribal bands with a lack of any clear central authority, governance being rooted in tribal assemblies. Rooted in honour – a vital concept in
Nordic pagantradition – violence was used as a measure to moderate disputes with other tribal groups. This emphasis on violence as a decisive tool regarding disputes was not limited to a man, but extended to his
kin.
[5] Violence was seen as a measure to defend honor. Honor was extremely important to
Norsemen, and the sense of shaming one's honor extended beyond physical and material injuries. Honor could be shamed from mere insults, where Norsemen were expected to react with violence often resulting in death. With this prevalence of violence came the expectation of fearlessness.