The basic plot derives from Beowulf, a heroic poem of unknown authorship written in Old English and preserved in a manuscript dating from around AD 1000.
Gardner's retelling, however, presents the story from the existentialist view of Grendel, exploring the history of the characters before Beowulf arrives.
The dragon plays a minor part as an omniscient and bored character, whose wisdom is limited to telling Grendel "to seek out gold and sit on it";[4] his one action in the novel is to endow Grendel with the magic ability to withstand attacks by sword (a quality Gardner found in the original).
Later, Grendel reminisces about his early experiences in life, beginning with his childhood days of exploring the caves inhabited by him, his mother and other creatures with whom he is unable to speak.
He goes on to recount an experience from his childhood, in which he found himself painfully wedged in a tree and threatened by humans, only to be saved by his mother.
During Hrothgar's rise to power, a blind poet appears at the doors of Hart, whom Grendel calls "the Shaper".
Grendel continues to mock Unferth until the thane faints from exhaustion, then takes him back to Hart to live out his days in frustrated mediocrity, thereby depriving him of the heroic death which he desired.
In the second year of his conflict with the humans of Hart, Grendel notes that his raids have destroyed the esteem of Hrothgar, allowing a rival noble named Hygmod to gain power.
Watching the Danes, Grendel hears a woman predict the coming of an illustrious thegn and then witnesses the death of the Shaper.
They wrestle furiously, during which Beowulf appears to become a flaming, dragon-like figure and repeats many of the ideas that the dragon espoused to Grendel.
The Pulitzer Prize-winning author Jane Smiley suggests that Gardner uses Grendel as a metaphor for the necessity for a dark side to everything; where a hero is only as great as the villain he faces.
Grendel lives in isolation and loneliness with his mother, who in her old age is unable to provide any real companionship to her child.
His long life grants him the ability to act as a witness to how their lives transpire and their behavior and logic bewilders him.
[9] Another Times reviewer, Richard Locke, declared the novel "an extraordinary achievement – very funny, original and deft, altogether lovable, poignant, rich with thought and feeling".
[12] It was given special mention by Diana Athill in her memoir Stet, covering her decades as an editor with UK publisher André Deutsch.
[14][15][16] In 2024 The Jim Henson Company announced that it was developing a live-action adaptation, directed by Robert D. Krzykowsi, with the title character being voiced by Jeff Bridges.
[17] The film also stars Dave Bautista as Beowulf, Bryan Cranston as King Hrothgar, Thomasin McKenzie as Queen Wealhtheow, Aiden Turner as Unferth, Sam Elliott as the voice of The Dragon, and T-Bone Burnett playing The Shaper and providing songs.
In 1982, the British neo-prog band Marillion recorded a 17-minute opus entitled "Grendel" that was based on the book.
[18] The American alternative rock band Sunny Day Real Estate recorded a song called "Grendel" that was based on the book and appeared on its 1994 first album, Diary.