What themes are illuminated by the characters?
While out walking, Browning made the comment to Hiram Corson, after the latter had published an introductory study of Browning's poetry, stating that what he had in mind when he wrote "gave orders" in "My Last Duchess" was the orders were for her murder [as an afterthought he also added an alternative for her to be "shut up in a convent"]. The Duke illustrates that one of Browning's themes in writing this dramatic monologue is that of Insolence. It is the tyrannical Duke's insolence that allows him to think that a viable solution to personal dissatisfaction with the whims of a young bride is murder. Insolence can be understood as haughty, arrogant, disdainful, contemptuous disrespect of personhood. Murder is the ultimate manifestation of disrespect of personhood.
Browning drew the inspiration for his poem from the Renaissance account of the Italian Duke Alfonso II d'Este of the Duchy of Ferrara, attested to by the one word epigram at the head of the poem: "Ferrara." In 1558 the 25-year-old Alfonso married the 14-year-old Lucrezia, the poorly educated young daughter the Midici family, then nouveau riche in comparison to the d'Estes of Ferrara. A poorly educated, fourteen year old bride unused to ancient tradition and manners of behavior would--upon suddenly finding herself the object of attention, esteem, wealth, and authority--be very likely to display giddy, light-hearted and universally delighted deportment.
Since the Ferrara marriage tale inspired Browning's poem--including the similar mysterious deaths of Lucrezia and the first duchess--it is logical to conclude that this is the true description of the Duke's bride whose blush of delight was awakened by trivialities as readily as by his passions. Through the character of the painted last Duchess, Browning presents the theme of Young Marriage, a practice popular in early epochs but fallen out of practice before the Victorian period, yet still envisioned in the wishful romanticality of the morally strict era.