According to www.dictionary.com, a monster is an imaginary or legendary creature [i.e. the boogeyman] having a strange or frightening appearance; an animal, plant or other organism having structural defects or deformities; one who inspires horror or disgust; any thing or person of unnatural or excessive ugliness, deformity, wickedness, or cruelty. Other words that can be used in substitution for the word monster - found on www.thesaurus.com - are beast, brute, savage, villain, barbarian, vandal, glutton, degenerate, and lusus naturae, which is a Latin phrase meaning a person or animal that is markedly unusual or deformed. Upon assessing the literal meaning of the word and the plethora of existing synonyms, several instances may be readily recalled from John Gardener's Grendel which clearly exemplify the narrator's monstrous temperament, including the narrator's physique, Grendel's relentless attacks on Hart and its people, and his twisted ponderings of existence.
One such example of Grendel's monstrosity is found where the reader is allowed to examine the character's most intimate inner thoughts: "Pointless, ridiculous monster crouched in the shadows, stinking of dead men, murdered children, martyred cows.
(I am neither proud nor ashamed, understand. One more dull victim...)" (6). In this passage, Grendel not only reveals that he has slain both men and children alike but also displays no remorse for the killings he has performed. In addition, referring to himself as a monster only predisposes the audience to accept such an opinion of the narrator.
A few pages later in the text, the reader sees an extension of the killer, as a glutton: "While they squeal and screech and bump into each other, I silently sack up my dead and withdraw to the woods. I eat and laugh and eat until I can barely walk, my chest-hair matted with dribbled blood"...