What are the similarities and differences between the villains in Beowulf and Sir Gawain and the Green Knight (by the Pearl-Poet)?
The villains in Beowulf are Grendel, Grendel's dam (mother) and the dragon that finally kills Beowulf—extremely evil characters who want to wreak havoc and destroy humans. The Christian influences in this surviving version of Beowulf blames the evil inherent in Grendel on the sin of Cain in the Bible's Old Testament.
Grendel was this grim beast called, who haunted the moors and secluded fens; this accursed one had long dwelled with monsters since the Creator had decreed his exile. On the kin of Cain did the sovereign God avenge the slaughter of Abel; Cain gained nothing from this feud and was driven far from the sight of men...From him awoke all those dire breeds: ogres, elves, and phantoms that warred with God a lengthy while...
Grendel he has been punished—separated from the company of man and God through the sins of Cain. This fuels his hatred, and a desire to destroy goodness from the world of which he can have no part.
When Beowulf fatally wounds Grendel, Grendel's dam returns for revenge. She is motivated by hatred—hoping to destroy the humans who have killed her son.
The hag came to Heorot, where the...Danes slept in the hall. The princes' old woes came back suddenly when Grendel's mother burst into their midst...That hag was in haste, wanting to flee with her life when the liegemen spotted her...she seized a single clansman [and] fled to the moors.
Beowulf and Hrothgar travel to retrieve Hrothgar's favorite—the liegeman the monster took. Beowulf valiantly fights and kills the dam.
Many years later—a thief disturbs the hidden treasure of a dragon that then attacks Beowulf's kingdom, killing his people.
When the dragon awoke...He immediately sniffed the scent along the stone. The dark-hearted one found the footprints of that foe who had walked undetected by the creature's head...The guardian of gold went tracking over the ground, eager to find the man who had brought mischief upon his slumber. Savage and burning, he circled 'round the barrow...he desired war and was eager for combat.
Beowulf valiantly saves his people, but dies from his wounds.
The villains in Beowulf are murderous. However, the Green Knight issues a challenge and Gawain accepts it in Sir Gawain and the Green Knight—but the giant has no wish to harm. He appears in Arthur's court at Christmas and issues a challenge: anyone can try to cut off his head. Young Gawain tries to do so; in failing, he is called to face the green creature in a year to give the Green Knight his opportunity to take Gawain's head, as a part of their agreement.
A year later, traveling to fulfill his promise, Gawain meets Bertilak (really the giant) and Lady Bertilak. He is tested secretly so Bertilak can see if Gawain is an honorable knight in Arthur's court. The giant spares Gawain, for he was honorable—only trying to trick the Green Knight in order to save his own life. But Gawain is appalled at his actions:
Oh knight: I humbly confess
My faults: bless me
With the chance to atone.
"I'll try to sin less."
Bertilak holds no grudge; he has convinced Gawain to work harder to be a worthy part of King Arthur's court.
Where Beowulf faces villains intent upon killing humans, Gawain faces a creature intent only in pushing the young knight to more fully know himself, so as to better serve his King.Additional Sources: http://www.enotes.com/sir-gawain-and-the-green-knight
Adventures in English Literature, Harcourt Brace Jovanovich Publishers: Orlando, 1985.