Grendel by John Gardner, is a retelling of the Anglo-Saxon poem, Beowulf in which Grendel is one of three main antagonists.
The book, Grendel, is told from the point of view of this antagonist. Gardner brings us, the reader, into the mind of the creature and helps us to truly understand his motives and reasons for his brutality and cruelty. With this version, the story of Beowulf is not a one-sided story. In Beowulf, Grendel is a flat character whom we do not like or understand. In Grendel, the opposite is true. We commiserate with him and see the story from his view--he is lonely, without companionship from even his mother, and he sees the Danes and the other humans he kills as his only "friends" or companions. We feel for him to the point that the hero Beowulf seems to be the brutal, cruel, and the one who does not understand.
The character of Grendel was not one of the major characters of Beowulf. John Gardner took the character of Grendel and wrote a retelling of the epic, using Grendel's side as the point of view. Previously, Grendel was seen as a vicious, soulless murderer, but here we see a vastly different depiction of the creature. Grendel is a thinking, reasoning, and soulful creature. He grapples with ideas of language and its uses.
The story is not told in a chronological fashion, but a mix of flashbacks and the present. The young Grendel becomes fascinated with language as a communication device, and learns to speak. He is especially enamored of poetry. Ironically, the blind poet used Grendel in one of his songs as the epitome of evil. It gives the men a lasting impression of Grendel. Grendel uses the power of language after his rampage of the men at the hall. While he has killed and eaten many men, he finds it useful to use his intelligence and words to hurt and degrade men in a different way.
The reflections of Grendel change the assumptions the reader had in the original epic, and make this character more sympathetic.