Gardner includes all featured characters from the original poem in his novel, but greatly changes many roles. Beowulf himself, for example, appears only in the last portion of the novel and has little dialogue or interaction with other characters. The author also introduces a handful of incidental minor characters.
- Grendel – the main protagonist and self-described monster, given the narrator's voice in the novel.
- Grendel's mother – another antagonist from Beowulf who lives in an underwater cave with her son. Unlike her son, she is incapable of speech and holds no curiosity of the world outside her cave.
- Beowulf – a Geatish hero who ultimately kills Grendel. He is never referred to by name in the novel.
- Hrothgar – warrior and king of the Danes.
- The Shaper – a blind harpist and storyteller in Hrothgar’s court.
- The Shaper’s assistant – the young apprentice who replaces the Shaper upon his death.
- Unferth – a Scylding warrior who challenges but fails to defeat Grendel.
- Wealtheow – queen of the Danes and wife to Hrothgar.
- Hrothulf – Hrothgar’s orphaned nephew.
- Freawaru – Hrothgar’s teenage daughter.
- Hygmod – King of the Helmings and Wealtheow’s brother.
- The dragon – an ancient, omniscient beast guarding a vast hoard of treasure to whom Grendel goes for advice. It possibly is a figment of Grendel's imagination. It is also possible the dragon was meant to be the same dragon that appeared in the epic poem Beowulf.
- Red Horse – Hrothulf’s elderly advisor.
- Ork – an old and blind Scylding priest.
Portrayal of Grendel
Pulitzer Prize winning author Jane Smiley suggests that John 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. Using Grendel’s perspective to tell at least part of the story of Beowulf in more contemporary language allows the story to be seen in a new light not only in terms of the point of view but also brings it into the modern era.
Where Grendel is portrayed mainly as a physical creature in the original work, here a glimpse into his psyche is offered. Grendel lives in isolation and loneliness with his mother who in her old age is unable to provide any real companionship to her child. As the only being of his kind, he has no one to relate to and feels the need to be understood or have some connection. Grendel has a complex relationship with the humans who hate and fear him. He feels that he is somehow related to humanity and despite his desire to eat them, he can be moved by them and their works. His long life grants him the ability to act as a witness to how their lives transpire and their behavior and logic bewilders him. He is cursed to a life of solitude, also being portrayed as having eternal life, which furthers his plight and loneliness as he can only fall in battle and he is immune to all human weapons. He is only freed from his tormented life through his encounter with Beowulf.