He seized one sleeping man, “biting the bone-joints, drinking blood from veins, great gobbets gorging down. Quickly he took all of that lifeless thing to be his food, even feet and hands.” How lovely, the bright-patterned floor. How appalling, Grendel’s dinner.

“Beowulf” is the story of the hero’s defeat of three successive monsters. The first is Grendel. The Geats are allies of the Danes, and Beowulf, who by then seems to be about thirty, decides to go to Denmark and rid it of this menace. It is hard to say what Grendel looks like. He is apparently about four times the size of a man. He has claws; he does not speak. But he also has human qualities. He has to enter Hearot by a door. When wounded, he bleeds, as Beowulf soon discovers. With his powerful hands, the hero grabs Grendel’s wrist and tears off his arm and shoulder. His shoulder! He then hangs the whole business—shoulder, arm, hand—from the rafters. Imagine the Danish knights drinking their mead as half of Grendel’s torso drips blood onto them. Grendel is the most real of the monsters. (It means something that he is the only one of the three who has a name.) As Seamus Heaney, another “Beowulf” translator, has written, Grendel “comes alive in the reader’s imagination as a kind of dog-breath in the dark.” Almost with embarrassment, you pity him somewhat. (Tolkien describes how, after the fight with Beowulf, Grendel, “sick at heart,” dragged himself home, “bleeding out his life.”) He is also a bit childlike. It is no surprise that John Gardner, in his 1971 novel “Grendel,” portrays the monster as a boy.

One reason Grendel seems childlike is that he has a mother. When her son comes home to die, Grendel’s mother goes on a rampage. So Beowulf must suit up again. The mother lives in a chamber below a stinking swamp: “The water surged with gore, with blood yet hot.” Beowulf dives right in, with his helmet on. His knights, afraid to join him, stand at the edge of the water. Grendel’s mother is waiting for him—with helpers, a gang of sea monsters, which tear at him with their tusks, to soften him up. Finally, she takes over. Demon or not, she clearly loved her son, and she goes at Beowulf with a blinding fury. The hero finds that his famous—and previously invincible—sword, Hrunting, is of no use against her plated hide. It bounces off her. But he sees, close by, another sword, forged by giants, which no man can pick up—except him. He waves it through the air, piercing the monster’s throat and breaking her neck bone. This is more horrid even than Beowulf’s removal of Grendel’s arm and shoulder, or, at least, it feels more painful. (It also shows a man killing a woman.) Before he leaves the den, Beowulf beheads Grendel’s corpse, lying nearby. Normally, the poet says, it would have taken four men to pick up that head. But Beowulf carries it alone, to the surface, and hands it to his knights. When they get back to the mead hall, they tug it around by its hair, as a game.

Beowulf’s third fight, which takes place back home, in Geatland, is with a dragon, who, unlike Grendel and his mother, is less a monster than a symbol. He is not sad or weird. Indeed, he is rather glamorous. He is fifty feet long and breathes fire. He has wings—he can fly—and he doesn’t live in a nasty fen. He has a nice cave, where he guards a treasure that has been his for three hundred years, and which he feels strongly about. But now someone has come and stolen a jewelled cup. This enrages him, and he begins incinerating the Geatish countryside.

Many years have passed since Beowulf killed Grendel and his mother. He has become the King of the Geats and ruled them for fifty years. He is about eighty years old now, and tired. Still, to protect his people he must eliminate this menace. He sets out, but “heavy was his mood.” Speaking to his knights, he reviews his great deeds. He bids them farewell. In what is probably the poem’s most iconic image, he goes and sits on a promontory that juts out over the sea. (This says everything. Beowulf will soon be part of nature—the land, the sea.) As always, he insists on going into the contest alone. His knights, relieved, slink off into the forest. The dragon emerges from the cave, “blazing, gliding in loopéd curves.” Beowulf brings his huge sword down on the monster’s body, but, as with Grendel’s mother, it doesn’t make a dent. The dragon sinks his teeth into the hero’s neck. His blood “welled forth in gushing streams.”

Will he lose the fight? No. Not all his men ran into the forest. One young knight, Wiglaf, stayed and, unbeknownst to the King, followed him close behind. Seeing Beowulf wounded, Wiglaf rushes forth and stabs the dragon “a little lower down.” As the poet is too polite to say, Wiglaf took better aim than Beowulf did, and thus weakened the dragon to the point where the old man could go in for the kill. Beowulf has not lost his touch: “he ripped up the serpent.” That’s the end of the dragon—the Geatish knights unceremoniously dump the body over a cliff—but it’s also the end of Beowulf. Wiglaf unclasps the King’s helmet, and bathes his wounds, to no avail. In the final lines of the poem, we see the knights, in tears, riding their horses in a circle around Beowulf’s tomb. “Thus bemoaned the Geatish folk their master’s fall, comrades of his hearth, crying that he was ever of the kings of earth of men most generous and to men most gracious, to his people most tender and for praise most eager.”

Tolkien may have put away his translation of “Beowulf,” but about a decade later he published a paper that many people regard as not just the finest essay on the poem but one of the finest essays on English literature. This is “ ‘Beowulf’: The Monsters and the Critics.” Tolkien preferred the monsters to the critics. In his view, the meaning of the poem had been ignored in favor of archeological and philological study. How much of “Beowulf” was fact, and how much fancy? What was its relationship to recent archeological finds?

Tolkien saw all this as an evasion of the poem’s true subject: death, defeat, which come not only to Beowulf but to his kingdom, and every kingdom. Many critics, Tolkien says, consider “Beowulf” to be something of a mess, artistically—for example, in its mixing of pagan with Christian ideas. But the narrator of “Beowulf” repeatedly says that, like the minstrels who entertain the knights, he is telling a tale from the old days. “I have heard,” he says. “I have learned.” Tolkien claims that the events of the poem, insofar as they are real, occurred in about 500 A.D. But the poet was a man of the new days, when the British Isles were being converted to Christianity. It didn’t happen overnight. And so, while he tells how God girded the earth with the seas, and hung the sun in the sky, he again and again reverts to pagan values. None of the people in the poem care anything about modesty, simplicity (they adore treasure, they count it up), or humility (they boast of their valorous deeds). And death is regarded as final. No one, including Beowulf, is said to be going on to a better place.