Willem Wolff Beffie (1880-1950) was a Dutch art collector, born in Amsterdam. He made his fortune in the diamond business at the beginning of the 20th century. Between 1912 and 1918 he acquired an impressive collection consisting of circa 500 works by international avant-garde artists like Franz Marc, Marc Chagall, Wassily Kandinsky, Alexei von Jawlensky, Marianne von Werefkin, Paul Klee, Kees van Dongen and Dutch artists Leo Gestel and Jan Sluijters. Beffie preferred to buy directly from the artists when visiting their studios, often being introduced by Franz Marc. During his lifetime he already sold works from his collection, now in the Guggenheim museum, Museum of Modern Art in New York and Stedelijk Museum in Amsterdam.