The speaker or voice of a literary work, or in plainer words, "who's doing the talking."  

             Sidelight: Sometimes the author of a poem identifies a created character as the speaker-- but in the absence of a specific attribution the term persona is applied in a neutral sense, since it should not be automatically assumed that a creative work directly reflects the personal experiences or views of the poet. The use of an identified persona precludes a potential ambiguity and enables poets to give expression to things they would prefer not to have attributed to their own person. 

             Sidelight: In Robert Browning's My Last Duchess, the persona is the Duke of Ferrara. In John Keats' Ode to a Nightingale, the persona is not identified, so it is up to the reader to infer whether it is the author himself or a speaker conceived by the poet for a particular effect. 

Reference: Glossary of Poetic Terms from Bob's Byway