The main character in "My Last Duchess" is the speaker, the Duke of Ferrara. He is a jealous, gloating psychopath who boasts to his visitor that he "gave commands" to stop his wife's flirtatious smiles. The Duke seems pleased that he has control over the Duchess now that she is dead. He is the one, after all, who covers and uncovers her portrait as and when he sees fit, and he is the one who decides what story about her his visitors hear.
While the Duchess was alive, the Duke didn't seem to have much control over her, and she would, at least as far as he could tell, flirt with other men. The Duke refused to even speak to his wife about his concerns, because even to do so would have been, he says, "some stooping," and he chose "never to stoop."
The main theme that emerges from Browning's presentation of the Duke and of his relationship with his wife, the Duchess, is the theme of gender inequality in the nineteenth century. The Duke seems to exercise all of the power, and he takes the life of his wife for nothing more than smiling at other men just the same as she smiled at him. She, on the other hand, is completely powerless. One symbol of this unequal power dynamic is the curtain which covers the portrait of the Duchess. The fact that he now has power to determine who sees her, and how they see her, indicates that he essentially has the power to determine how she is remembered, or if she is remembered at all.
The second key symbol which demonstrates this theme of gender inequality is the statue that the Duke points out to his guest at the end of the poem. The statue depicts "Neptune . . . Taming a sea-horse," which symbolizes the Duke taming the Duchess. Compared to the Duchess, represented by a small sea-horse, the Duke is a god, like Neptune.
This grossly unequal power dynamic is a reflection of the respective positions of men and women in Victorian England. When a woman married a man, for example, all of her legal rights, as well as all of her property, were transferred to the husband. A husband and wife were considered one body, represented by the husband.