What is the fascination with evil? In Beowulf, why is Grendel (a man or a woman?) more interesting than Beowulf?
Grendel is neither a woman nor a man; he is a monster, a demon, and a fiend, a creature separate and apart from humanity:
He was spawned in that slime [of the moors and marshes],
Conceived by a pair of those monsters born
Of Cain, murderous creatures banished
By God, punished forever for the crime
Of Abel's death.
Thus Grendel was born of evil itself and acts as its agent. He was born of "a brood" who forever work against "the Lord's will" and who are "again and again defeated."
Grendel's evil is not found in his abhorrent physical characteristics but in his nature and intent. He loathes God, God's followers, goodness, love, light and human companionship. He delights in murder and destruction, attacking Herot merely for the pleasure of destroying the sleeping warriors and their community. As the result of Grendel's hatred and rage, Herot remains deserted for twelve years, "[t]welve winters of grief for Hrothgar."
Why we are so fascinated with Grendel and the evil he brings into the story is an interesting question. Perhaps we find him fascinating because he is the exception, not the norm. Grendel is unlike all others in the story, with the exception of his own mother, also a monster. He is unusual, to understate the case, with his terrible claws, magic skin, superhuman strength, and stealthy form. Perhaps we are fascinated with Grendel because he symbolizes anything or everything that threatens our own safety and security. Speaking idealistically, perhaps Grendel fascinates us because we are good and find his evil simply incomprehensible.