One of the earliest Viking Kings we know about is Ongendus, Angantyr. He comes down to us in the sources as "fiercer than a wild beast and harder than a stone." Ongendus reigned in the early 8th century. Some credit him with beginning work on the Danevirk, that massive earthen wall that guarded the neck of the peninsula that leads to Jutland, Denmark. There is no evidence that Ongendus worked on the Danevirk however; archeological evidence dates some work on this wall to the mid 8th century. We do no he accepted a Christian missionary from Northumbria nad allowed him to take some people back to Nothumbria with him. It is from this missionary that we have our impressions of this King.
My guess he was a big, bearded fellow, filled with mirth and wrath. He was physically imposing and loud; probably didn't listen to the reasoned arguments of his visitor which led to his description. Probably lived in a great wooden hall and commanded a host of like mind vikings who, like him, drank, feasted and made merry.