The speaker in this poem is almost, but not quite, a fully-fledged character; he’s somewhere between the shadowy impersonal speaker that we assume is between the poet and the poem every time we read poetry and find an actual character who interacts with other characters in the poem. Even before the speaker starts talking about himself by saying, "I this" and "I that," we know that there is a speaker here. Not only does every poem have a speaker, but this speaker is addressing the West Wind, calling it "thou" and invoking its aid. That must mean there’s someone doing the invoking, someone talking to the "thou" – an "I." In fact, we could make that a rule: for every "thou," there’s an "I" lurking somewhere.
We know that this speaker is concerned about sending his ideas out into the world for other people to experience. He knows, or thinks, that his ideas aren’t any good; in fact, he describes them as "dead" and "withered." But he still wants to get them out there, because they might provide an opportunity for other people to develop their own ideas. He feels incapable of doing this on his own because of something that has happened to him. It might be some specific traumatic thing, but it might just be the general pain of living. He only refers to it as "the thorns of life" (54).
We also suspect the speaker might be a writer or even a poet, because he likes to pun on the word "leaves," which could be things that fall off trees but could also be pages of books. He also refers directly to the poem itself within the poem: "by the incantation of this verse / Scatter...my words among mankind!" (65-6, 67). So it’s not just Shelley writing a poem about this speaker – the speaker himself knows about and is composing the poem.