Birillo, born in 1928, was known early on more as a collector than an artist. By the early ’60s, he had amassed an impressive collection of Pop art—one that rivaled only that of his friend, Castelli, who at the time was considered to be the most influential gallerist in the world. Birillo—who was working in advertising at the time—would often sell work through Castelli, so much so in fact that the venerable collector often referred to him as the “Castelli Annex.” It was Castelli who encouraged Birillo to show his own work, organizing a show with him and his close friend, Andy Warhol.