Within Beowulf the character of Grendel is presented to us as a figure that imposes violence and is a major threat to the people in Hrothgar's kingdom. Although in the novel Grendel the character is presented in a much different manner. Gardner writes through the perspective of Grendel himself giving us an insight to what Gardner believes are the reasons that Grendel continued to show up at Hrothgar's mead-hall countless times before being killed by Beowulf. It seems that Gardner wanted to show us the kinder side of Grendel and wanted us to see that even the so-called villians in any story aren't entirely evil.
At the start of the novel Grendel Gardner makes Grendel seem as though he believes himself to be better than the other creatures he encounters and also he thinks of them as simply mechanical, just responding by instinct rather than thinking about what they are doing. One main difference seen in Grendel's character from Beowulf is that Grendel is now shown as simply curious of the humans because it is his first encounter with them. In Beowulf though Grendel is just a terrorist to the Danes and even the audience is almost told to hate him through the ways that the author of Beowulf describes him and his actions upon Heorot and the Danes.
During Grendel's first encounter with the Danes he is scared of them and realizes that they are not just mechanical like he first had thought, as he thinks about every other creature in the start of the novel. We see him making an effort to befriend the Danes, but because of a lack of communication the Danes misinterpret his efforts to speak to them and take him on as a threat rather than a friend. This, as seen in Grendel, is what causes Grendel to start coming into the mead-hall and killing and eating some of the Danes that are feasting there. When he encounters Beowulf in the novel Grendel he is shocked at the strength of him whereas within Beowulf we have nothing telling us what Grendel is thinking upon this meeting. Contrary to what we are made to believe in Beowulf, Grendel doesn't like killing the Danes but because of how they treated him he feels forced to act that way in order to prove himself.