Speaker
The speaker is quite likely Williams himself, based on known biographical details surrounding the poem. He is characterized by the straightforwardness of his diction and the authentic quality of his sentiments. He honestly expresses his regret over having eaten the plums, but remembers their pleasing taste. Throughout the text, he is torn between these feelings of remembering the plums and recognizing the unkindness of what he was done. The voice he employs strongly resembles that of a note from a spouse or domestic partner, left on the kitchen counter.
Speaker's Wife
Though absent in the poem, the speaker's wife (again, likely Williams's wife, Flossie) is the addressee of the piece. There is a tenderness suggested between her and the speaker in the regret he expresses over this relatively small deed.