Mathilda’s father considered her “unmarriable” due to a hideous growth on her back, and wished that she’d focus on more wifely pursuits in favor her passion for writing. After his death however, she was taken under the wing of Oscar Wilde who nurtured her skills for writing pretty tales for children. However, Mathilda had developed a taste for the darker side of life, specifically the works of a macabre painter named Roisin Dubh. Mathilda longed to meet Roisin, and hoped that Oscar Wilde, their mutual acquaintance, would introduce them at a party.
In truth however, Mathilda Thorne was Roisin Dubh. Her dependence on laudanum coupled with her repressed nature, lead to her leading a double life in her sleep. By day she was the prim and proper Mathilda, but by night she would go out and engage in debauchery as Roisin.
She doesn’t realize this herself until The Corinthian, in his function as the dark mirror of humanity, haunts her dreams and shows her what she truly is.