A monster is defined as something which inspires horror and disgust and is shockingly hideous or frightful. The characters of both males in 'Porphyria's Lover' and 'My Last Duchess' definitely give the impression of fitting this description, as they both commit, or at least command the committing of murders. They are also controlling of the women in their lives and crave power over them – in both cases, the woman behaving in a way the man does not approve of is the reason for their demise. The characterisation of these men as monsters is further justified by their lack of remorse for their acts; the man in 'Porphyria's Lover' argues that it was for her own good, and the man in 'My Last Duchess' is proudly recounting his actions to an envoy, showing he does not regret what he has done. The only possible redeeming feature of the man in 'Porphyria's Lover' is his insanity, as it could be argued that due to his mental instability he is not responsible for his own actions, and perhaps in 'My Last Duchess' the Duke may feel a shred of guilt for what he has done, which would not redeem him, but would make him less despicable and monstrous.
It is immediately obvious that the men in both poems are violent and murderous; in 'My Last Duchess' the man “gave commands” so “all smiles stopped together”, implying that he ordered his wife to be killed. The fact that commands were given for this to happen shows he considered his actions beforehand, and still decided to go ahead with the murder of his wife. The crime of his wife was to flirt with other men, a small crime for such a huge, permanent punishment. Her pleasure in flirting with other men is shown by the “spot of joy” which she called up, the the Duke's view of this his made clear through the use of the noun “spot”, which connotes a blemish, a mark on her otherwise good character, and something disgusting which the Duke does not like.