The Speaker

The speaker appears only once at the poem, at the very beginning, to situate readers in the text. The speaker reports a "dream, that was not at all a dream" (1-2). After this initial introduction, the speaker never reappears, so all that we know about him is from his dream. He is obviously quite a pessimistic, even a depressive character, with a powerful imagination.

Humanity

In Byron's lifetime, this poem was often grouped with a subgenre called "last survivor" poems, which show one person persisting in the apocalypse. This is obviously quite inaccurate for this poem, where there is no lone survivor. Instead, humanity is categorized as a group: one single mass of doomed misery. Humanity is generally described in broad terms, addressing the entire population, and described with collective nouns.

The Dog

The only figure that is separated from this mass of suffering is, in fact...