Guglielmo Achille Cavellini (11 September 1914 – 20 November 1990), also known as GAC, was an Italian artist and art collector. After an initial activity as a painter, in the 1940s and 1950s he became one of the major collectors of contemporary Italian abstract art, developing a deep relationship of patronage and friendship with the artists. Cavellini resumed his activity as an artist, with an ample production spanning from Neo-Dada to performance art to mail art, of which he became one of the prime exponents with the Exhibitions at Home and the Round Trip works. In 1971 he invented autostoricizzazione (self-historicization), upon which he acted to create a deliberate popular history surrounding his existence through self-promotion. He made 16 Manifesti (Posters) for the exhibition that he imagined would take place in 2014 in the most important museums of the world to celebrate the centennial of his birth. In 1972, Cavellini created the first Francobolli (Stamps) that showed his portraits: first that by Mario Ceroli, then those by Mimmo Rotella, James Collins and Andy Warhol. He also made seven self-portraits which he transformed into stamps to celebrate his centennial, and he also exhibited them at the Segnapassi Gallery in Pesaro. He also created 25 covers for the books that the most important people of the past and present time would have written about him.