In the epic tale of Beowulf and John Gardner's novel called Grendel, the most striking difference is Gardner's decision to have Grendel tell his own story, thus making the monster a more sympathetic character.
In Beowulf, Grendel's entrance into the mead hall, repeated as he has done for twelve years, is described as he moves with seething anger intent upon grabbing and devouring his first victim. He is thrilled to see such a collection of mighty warriors. The iron on the doors cannot stop—he moves with "furious rage." His "heart laughs" when he thinks of ripping the soul from the body of his victim.
THEN GRENDEL CAME from the moors by way of the misty crags; God's wrath lay heavy on him. The monster was of a mind to seize a human in the noble hall...This was not the first time that he'd sought Hrothgar's homestead, but never before had he found such mighty warriors, such guardians of the hall.
The accurséd rogue then came to the hall; the door opened when his fists struck it, even though it had been fastened with bolts of iron, and he ripped open the house's mouth in his furious rage. He then quickly tread over the paved floor, his ire streaming like flashes from his eyes, like a flame. He spied the band of heroes in the hall, the hardy liegemen, that group of clansmen gathered together sleeping. Then his heart laughed, for the savage beast was in the mood to sever each soul's life from its body before daybreak as he saw this opportunity to sate his slaughterous appetite.
However, in Gardner's novel, Grendel (the narrator) paints the picture of a pitiful creature that is bullied by animals in the forest. He has been hunted by men—men who do not leave, but build a grand mead hall. Grendel describes the dragon's victimization of this young "creature."
Grendel claims that he originally does not want to fight. Unferth, who drunkenly criticizes Beowulf when he arrives at Hrothgar's mead hall in the poem, attacks Grendel in Gardner's novel. Grendel evades Unferth, but retaliates, throwing apples at him—thus humiliating Unferth. This depiction promotes the emerging image of Grendel as a battered, misguided child.
The Shaper (storyteller, scop) arrives at the mead hall and tells stories of Grendel: descended from the line of Cain—the first murderer. The dragon further twists Grendel's mind. One night Grendel approaches the mead hall and a guard tries to kill him. In that moment Grendel discovers that the dragon has put a spell on him—mankind's swords cannot harm him. He grabs the guard, and rage bursts forth from the monster directed at all of mankind.
Then, little by little, I understood. I felt laughter welling up inside me—at the dragon-charm...at everything—the oblivious trees and sky, the witless moon. I'd meant them no harm, but they'd attacked me again, as always. They were crazy. And now at last the grim laughter came pouring out, as uncontrollable as the dragon's laugh, and I wanted to say, "Lo, God has vanquished mine enemies!"...
Grendel takes the guard, still living, and in front of the gathered members of the hall, eats the man starting with his head. Taking what is left of the body, Grendel flees "with glee" into the woods, experiencing "unearthly joy." And so his raids on the hall begin.
In Beowulf, the hero comes to battle a crazed monster that has been haunted the hall and murdering for years. In Gardner's novel, Grendel describes himself as a product of his environment—driven to violence—but still a monster.