Speaker

Def:
Speaker is the person who tell the stories in a poem, however, a poet and a speaker are not always the same. Because not every "I" in the poems are the words of the poet.
Examples:

The Road is not taken by Robert Frost

Two roads diverged in a yellow wood, And sorry I could not travel both And be one traveler, long I stood And looked down one as far as I could To where it bent in the undergrowth; Then took the other, as just as fair And having perhaps the better claim, Because it was grassy and wanted wear; Though as for that, the passing there Had worn them really about the same, And both that morning equally lay In leaves no step had trodden black Oh, I kept the first for another day! Yet knowing how way leads on to way, I doubted if I should ever come back. I shall be telling this with a sigh Somewhere ages and ages hence: two roads diverged in a wood, and I -- I took the one less traveled by, And that has made all the difference.

=> The "I" that the author is using may describing an experience of the speaker but not the poet.

Sign:
Poet doesn't have to feel the same as the speakers. Assuming that the poet is saying something that he/she has not experience her/himself would be more creative because the speakers make up a character that is not the poet.