Grendel

Grendel is described by Seamus Haney as a human like being but larger there really is not a good description on how he looks until they rip his arm off then we can infer that he is like a lizard type character,"Every nail, claw-scale and spur, every spike and welt on the hand of that heathen brute was like a barbed steel. Everybody said there was no honed iron hard enough to pierce him through, no time proofed blade that could cut his brutal blood caked claw", line 983-989 page 61. In the movie by Robert Zemeckis he is portrayed as a zombie like character. He is actually the son of King Hrothgar and you can infer that the motive that he attacked the hall is because King Hrothgar did not want him and did not want anything to do with him.