The hero of the Anglo-Saxon epic Beowulf is, of course, Beowulf; the first of his three nemeses is Grendel. The two of them do not have much in common, but there are several points of comparison.
While Beowulf is a well loved thane committed to the service of a king, Grendel is a loner who wanders the moors and fens, mostly alone. While Beowulf is eager to selflessly serve others, Grendel "nurse[s] a hard grudge" and is enraged to see anyone at Heorot (or anywhere, really) having a good time. While Beowulf is a normal-sized human being, Grendel is some kind of huge monster (remember how big his head is), complete with talons and scales. While Beowulf carries a sword and shield and wears chain mail, Grendel relies on a spell he cast on himself which will ensure that no sword can do him harm. While Beowulf's motivation is altruistic, Grendel seems motivated by evil.
Though these two seem to be nothing alike, they do have at least two things in common. First, they are both willing to kill, though their motivations for killing are quite different. Second, their arm strength is equal. Beowulf is known to have the strength of thirty men in one arm, while Grendel can carry thirty men away from the mead-hall before eating them.
When Beowulf meet in hand-to-hand combat, then, it is an even match which Beowulf wins.
The captain of evil discovered himself
in a handgrip harder than anything
he had ever encountered in any man
on the face of the earth. Every bone in his body
quailed and recoiled, but he could not escape.
He was desperate to flee to his den and hide
with the devil's litter, for in all his days
he had never been clamped or cornered like this. (749-756)
It is true that Beowulf's and Grendel's motivations and passions are quite different; however, the few things they have in common make them well matched opponents.