The character Grendel in both works Grendel and Beowulf portray him in different lights. Due to different times there are different cultures and styles of writing intermingled in the works. Grendel is an angry character; however, due to the different eras, the types of anger are distinguished and this enables the character to be undeveloped as well as developed simultaneously.
In Grendel, he relieves his anger with his need to spy. He sits in the woods all the time just observing the different tribes in the woods. He sees how the people treat each other so coldly and this brings him to more of a realization about himself and his own temper and anger management. Grendel realizes that he is alone in the world and only has his mother to aid him in difficult situations. In Beowulf, Grendel has no way of relieving his anger; "No wolf was so vicious to other wolves" (page 32). When he hears the music of the harp, he just howls in pain, which was an automatic reaction of evil. When Grendel attacks the mead hall and eats everyone in it, he has no reason for doing this, he basically does it because he is purely evil.
The way the two characters are described physically, also gives the two stories completely different spins. In Grendel, Grendel is characterized as a ridiculously hairy creature. This brings a sense of comic relief to the story. In Beowulf, Grendel is just described as an angry monster, who has no feelings, "Grendel was spawned in that slime" (page 19). The slime gives a sense of evil that was the essence of Grendel.
In Beowulf and Grendel the character Grendel hides in the woods. In Grendel, the character does this because he uses it as a means of control. Almost "out of sight out of mind" in a sense. In Beowulf, his hiding in the woods shows his cowardly side. It is his place of seclusion from the outside world around him. It masks his fear of being hated and feared by everyone.
Grendel makes Grendel a self-understanding creature.