Rendela incurable monster or a extremly vicious man?

Grendel–a descendent from Cain who lives under an inherited cursedisrupts the joyous and peaceful mead hall of Heorot and commits various murders without apparent provocation. We can argue that the Beowulf-Poet succeeds in giving the figure of Grendel his memorable power precisely by keeping him flickering in that half world on the edge of the human–far away from mankind, yet an essential part of him. In your estimation, what foremost characteristics of mankind are revealed in the poets representation of this monster?

Added on 20.02.2015 06:11
Do Grendels mother and the Dragon serve similar purpose?