The poem also mentions various and sundry other undesirables such as giants and monsters, but Cain is the most ominous ancestor.  This is ancestor is chosen to make more clear the Anglo-Saxon loyalty to family and kings.  Those to whom you are related and to whom you pledge your life are bonded...however, Cain is considered the most evil because he rebuked that bond.  Anyone who commits this crime in Anglo-Saxon times and literature is usually considered an outcast...therefore, Grendel, being descended of this murderer, is the ultimate miserable outcast.  And so, the setting/background info is laid for the remainder of the poem.  Good Luck, and happy reading!

Cain. The Bible refers to Cain being \'marked\' as punishment for killing his brother, Abel. Over time many people have interpreted this \'mark\' as different things. The monk writing \"Beowulf\" down from the ancient oral epic wanted to incorporate Christian elements into the original pagan story. So he obviously added this element to make Grendel an agent of the devil. The play, especially the scenes with Grendel, are filled with Christian allusions.

For an interesting view of Grendel check out Ben Gardner\'s novel \"Grendel,\" which tells \"Beowulf\" from Grendel\'s point of view.

Grendel is a descendant of Cain, the world's first murderer.

Grendel and his mother are once again referred to as descendants of Cain, the biblical "kin killer." It says, "From him (Cain) sprang many a devil (monsters such as Grendel and his mother) sent by fate." (Norton, page 43.)