Who was finn? What was his story? Why would the Anglo-Saxon author include this?

Finn was the King of the North-Frisians and the Jutes. He was married to Hildeburg. During his reign there was horrible slaughter at his court, in which the Danish general, Hnæf, was killed. Finn was later slain by Danish warriors.

I'm not sure why this was included outside of the fact the author or storytellers were providing historical information about the relationship between the Frisians and the Danes.