Eleanor Johnson in Public Books:
Scene: Scandinavia, late summer, a cloudless night. The Dark Ages. Seemingly from nowhere, a quasihuman monster, descended from Cain, hears the sounds of warriors reveling in their Great Hall and decides to silence them. Creeping out of the unstructured darkness of his usual stomping grounds, this monster sneaks into the Great Hall and slaughters the warriors in their sleep. The monster develops a taste for blood, so these murders become habitual. For years.
When the monster is at last maimed and slain by a hero, his semihuman mother creeps out of the fetid pond they live in to take revenge for her only child’s death. She rips men apart in the night, seething like death itself. The same hero follows this grim hag into her pond (he’s a strong swimmer) and cuts her down with a talismanic sword. Some time later, a third monster surges forth, this time a poisonous dragon. The hero kills the dragon, too, but not before the dragon lethally poisons him.
All that is left is horrified lamentation at the certainty that worse things are coming. Despite the hero’s efforts and sacrifices, no one is safe. The women ululate, and the rituals of burial for the hero bring no comfort.
This is the story of Beowulf. And, to the best of my knowledge, it is the earliest horror narrative in English literature.