Originally penned by the mystic Cagliostro in the 1780s, il Libro di Cagliostro (lit. "The Book of Cagliostro") is an account of Cagliostro's personal history, and a collection of mystic knowledge gathered from numerous sources, including passages of the Darkhold, notes from 31st century sorcerer Sise-Neg, as well as Cagliostro's own considerable knowledge.
Followers of Cagliostro were entrusted with guarding the book, which was passed down through the generations. It would come into the possession of a woman named Miarka, the mistress of Nikolai Mordo, who passed it to her daughter Lilia, who then passed it to her daughter, Lilia Calderu. Calderu would eventually be seduced by Karl Mordo, who then assaulted her and stole the Book of Cagliostro, hoping to use its power to defeat the Ancient One.
Mordo would eventually use the Book to travel back in time, hoping to convince a time-displaced Sise-Neg to take him on as an apprentice. Hoping to stop him, Calderu would help Dr. Strange track down the Book, which Strange used to track down Mordo.
The fate of the Book of Cagliostro after Strange used it to travel back in time is unknown.
Alternate Reality Versions
Marvel Cinematic Universe (Earth-199999)
The Book of Cagliostro lay secure in the library of Kamar-Taj as part of the personal collection of the Ancient One, who had used the knowledge contained within to prolong her life for centuries. One night, Kaecilius entered the library, killed the librarian, and stole pages from the ancient tome. His purpose was to uncover the secret of communing with Dormammu, a being of immense power from another dimension. Initiate sorcerer Stephen Strange came across the book himself and began applying some of its content to make use of the Eye of Agamotto. He was interrupted in this task by Karl Mordo and Wong, both of whom knew the dangers he was toying with. The Book of Cagliostro was returned to its rightful place, although Strange later had reason to use its knowledge again when he and the others finally confronted Kaecilius.