Poems were passed down through generations verbally by traveling performers called scops. Accordingly, alliteration became a significant tool used as a memory aid.

For example, the poet describes the joyous celebrations in the great feasting-hall until the evil fiend Grendel attacks and destroys the serenity:

A powerful monster, living down
In the darkness, growled in pain, impatient
As day after day the music rang
Loud in the hall . . .
So Hrothgar’s men lived happy in his hall
Till the monster stirred

This pattern is used throughout the poem. Beowulf is described as a great warrior of the Geat tribe in Sweden and the strongest of men. Grendel is described as a hellish monster—not animal but a very primitive human descended from the biblical Cain. Grendel’s mother, who lives at the bottom of a lake housing monsters, is described as a vengeful creature brooding over Grendel’s death. In each case, the poet interjects alliterative verse to highlight the characters’ demeanors, qualities, and actions.

The Beowulf poet employs alliteration instead of rhyme to somewhat emphasize the qualities and actions of the characters. While he does use alliteration to heighten the contrast between the actions of characters like Beowulf, Grendel, and Grendel’s mother, the literary device is primarily used to connect the narrative structure of the poem.

First, because Anglo-Saxon poets tended not to use rhyme--particularly end rhyme--in their poems, which is a technique poets use to connect lines together in order to help the poet recite a poem to the audience (keep in mind that Anglo-Saxon poetry began as an oral tradition, not written), Anglo-Saxon poets employed initial rhyme, also known as alliteration.  Second, the primary effect of the repetition of initial sounds is to "move" the speaker and listener through a line of poetry quickly--think of it as a wave moving from left to right--partly to enhance the listener's ability to memorize a poem. Third, because of its usefulness, alliteration became over time an expected feature of Anglo-Saxon poetry.  More specifically, each pair of half lines had to be connected by alliteration.  For example, in the first few lines of Beowulf, we have

Beowulf was well known    wide-spread his fame--
the son of Scyld              in Scandinavia (ll. 18-19)

In this example, in the first two half lines ( each called a hemistich), we have the initial w sound four times in seven words, and in the second, we have initial s sounds in three words in a six word line.  The alliteration, one can argue, encourages forward movement for both the speaker and the listener because it creates rhythm (without rhyme).

Given the fact that alliteration is an expected component of all Anglo-Saxon poetry--and that it is a technique to create rhythm without rhyme--it is difficult to argue that alliteration itself is used to differentiate characters. Certainly, alliteration enhances the description of characters, their speech, and their actions, but alliteration enhances description (of place, for example) and narrative in exactly the same way.

In sum, then, alliteration has important effects in Anglo-Saxon poetry in general, but its effects--particularly its creation of rhythm--are not specific to individual characters in the poem.