Guglielmo Libri Carucci dalla Sommaja (1 January 1803 – 28 September 1869) was an Italian count and mathematician, who became known for his love and subsequent theft of ancient and precious manuscripts.

His friend Arago, the secretary of the Académie des sciences helped him obtain a professorship at the Collège de France in 1833, succeeding the great mathematician Legendre.

[4] His original research was partially based on some 1800 manuscripts and books by Galileo, Fermat, Descartes, Leibniz, and other luminaries which he claimed to have collected throughout his career; in fact, some of these, as it turned out, had been stolen in Florence from the Biblioteca Medicea Laurenziana.

Abusing his privileges and pretending poor health (coughing, dressed in a big cape in all weathers), he managed to spend time alone in the archives of libraries across the country.

Thanks to the blind confidence of the canon Hyacinthe Olivier-Vitalis, he seized at the Inguimbertine library of Carpentras numerous documents such as the " Works of Théocrite and Hésiode " (Venice, Alde, 1495) or 72 of 75 letters of Descartes to Father Mersenne (between 1837 and 1847).

In London, he was assisted by Antonio Panizzi, the Director of the British Museum Library, and was able to convince many that his problems in France had arisen because he was an Italian, not because the allegations against him had any substance.

Mérimée, the author among other stories and plays of "Carmen", had been convinced of Libri's innocence when the Count had told him that the missing French books and manuscripts must have been forgeries since the ones he had were the originals.

In June 2010, one of the stolen items, a letter from Descartes to Father Marin Mersenne, dated 27 May 1641 and concerning the publication of “Meditations on First Philosophy”, was discovered in the library of Haverford College in Pennsylvania, United States.