What is the relationship between Unferth and Hrothgar?

Unferth is a thane in Hrothgar (a nobleman of sorts). He has some contempt for Beowulf and engages him in a boasting match, which he loses. It is not that Unferth doesn't help defend the hall against Grendel in the current events of the poem, but Beowulf brings up in the boasting match that Unferth has done nothing to stop the creature thus far (Grendel has been coming regularly to the hall to wreak havoc).

Unferth is a bit jealous of Beowulf; it's one of those relationships where the new guy has to prove himself. Unferth has done his best to battle Grendel, but he and the other men have come up short time after time; Beowulf uses this fact to antagonize him. Once again, Beowulf is the "new" challenger, and although he is well respected in his homeland he has something to prove.