who as the speaker of the my last duchess

The speaker of the poem is an Italian Duke who's showing an emissary from another court the portrait of his late wife. The emissary has been sent by his master, the Count, to the arrange the marriage of his daughter to the Duke.
One hopes that the unfortunate young lady will escape the tragic fate of her predecessor, for the previous duchess was killed on the orders of the Duke. As he shows the emissary the last duchess' portrait, the Duke expresses his exasperation at the way she bestowed her thanks and smiles on all and sundry. This made the Duke feel somewhat less than special, as if he were being placed on the same level as everyone else. To someone of the Duke's high social status, this was an outrageous insult to his honor and so, dissatisfied with his wife, he arranged to have her killed.
https://www.poetryfoundation.org/poems/43768/my-last-duchess