How does Unferth serve as a foil to Beowulf?

Unferth is the opposite of a kick ass viking warrior alpha male. He is jealous and he seeks to disparage Beowulf with weak words and gossip like innuendo. Unferth really hasn't delivered on killing Grendel so he resorts to bad mouthing Beowulf. Beowulf on the other hand is a man of action. He creates his own legacy.