In The Tale of Despereaux Botticelli's character personifies pure evil, unfettered by a conscience. Other characters in the story display evil qualities and tendencies, but nearly all possess some goodness as well. Botticelli is a rat who is evil to his core. He is described as old, one-eared, and vaguely hypnotic. 

"The meaning of life," said Botticelli, "is suffering, specifically the suffering of others."

These lines from chapter 16 encapsulate the villainy of the character. However, Botticelli isn't just a personification of evil in the story; he is also a reflection of the darker nature of Roscuro. Nearly every name in this book tells the reader something of the character in question. The Princess Pea was named after a legume commonly found in soup, which is one of her mother's favorite foods. Despereaux was named "for the many despairs in this place."

Roscuro's full name, Chiaroscuro, means "the arrangement of light and dark," specifically in relation to painting or drawing. Botticelli is the name of a famous painter. If the rat Chiaroscuro is a contrast of light and dark, then his friend Botticelli is the painter who shapes him. Botticelli encourages Roscuro to seek revenge and to make the princess suffer. Botticelli's last name is Remorso, and while the rat never experiences the emotion himself, Roscuro's darkness does, in the end, give way to remorse. 

Ultimately, Botticelli Remorso's name is more prophetic and indicative of Roscuro than of the one-eared rat himself.