Most fundamental human qualities are displayed by Grendel. He was an intelligent monster with the irrational thoughts capability. He shares the lineage with the human being, as being a descendant of the biblical Cain. Very little separates him from other human beings due to his nasty eating habits and awful appearance. Moreover, he accentuates the inherent violence of man. This highlights his philosophical quest is of human-like. By the wasteful war he feels disgusted on the other hand he is easily upset and cautious.
Grendel's relationship with the humans is characterized by the emotional response to the concept of community. Grendel is frustrated with the world he is living in, the animals that surround him are dumb and undignified. Further, that his mother is driven by the emotional instincts. Therefore, Grendel is trapped in his own world where he performs one-way communication by talking to the sky or air with no response.
The human who resembles Grendel in many ways, most painful refusal comes from them as they fret and disgust to share any meaningful conversation with Grendel. Yet Grendel, so close to humankind he is kept at a distance.
Therefore, Grendel is modern day monster rather than a traditional, historical monster in a way that Grendel grapples with trying to understand the meaning of life.