Giuseppe di Cattivo

Giuseppe di Cattivo was a contemporary of Leonardo da Vinci and a fellow artist, as well as his neighbour.

Biography
Giuseppe di Cattivo was renowned for the disturbing nature and morbosity of his paintings, for which he became known as "The Artist of Nightmares". At one point in his life he found a sentient metiorite and used its minerals as a material for his pigments. Using this paint he created his masterpiece, called The Abomination, and lent some of it to da Vinci for one copy of the Mona Lisa (the copy that would eventually be found in the Louvre, Paris). The Abomination however was too terrible to lay eyes on without going mad. Gripped by fear, di Cattivo locked the painting in a vault made of wood from the hangman's gallows, with a Chinese Puzzle Box acting as the lock. The following morning, he was found in his Florence apartment, completely insane.

The International Gallery of London took possession of a collection of his works in Victorian times, and stored them in the vaults in the basement. (SJA: Mona Lisa's Revenge)