Grendel' strength is evident in the description of his first attack on the Danes, when he takes thirty men in one fell swoop with him for a "banquet of bodies." As well, the fact that Grendel's reputation travels as far as to reach Beowulf means that Grendel's strength is famed, and he is a creature so terrifying that word has traveled quickly amongst the humans in the general vicinity.
From the start of the poem, Grendel's evil intentions are made clear by his kinship with other demonic creatures. In lines 100–110 of the epic poem, the speaker emphasizes Grendel's clear association with "the kin of Cain" and with the "unspeakable offspring" of Cain's clan. This connection with "ogres and elves and spirits from the underworld" makes Grendel evil by inheritance. As well, Grendel's first attack on the Danes takes place at night, while they are sleeping. His decision to attack while the Danes are vulnerable suggests that he does not fight honorably, a choice which emphasizes his evil nature.