Who is the speaker in the poem, To Althea, From Prison?

The speaker is a prisoner, both literally and metaphorically. He is himself a poet of sorts, choosing elaborate, symbolically rich language to describe his experiences of imprisonment. He is also an ardent monarchist, a supporter of the king and a defender of his cause. He is proud of his beliefs, and of his own courage in standing up for them even as they become politically unpopular and personally dangerous.