Hopper began working as a painter and a poet as well as a collector of art in the 1960s as well, particularly Pop Art. Over his lifetime he amassed a formidable array of 20th- and 21st-century art, including many of Julian Schnabel's works (such as a shattered-plate portrait of Hopper); numerous works from his early cohorts, such as Ed Ruscha, Edward Kienholz, Roy Lichtenstein ("Sinking Sun", 1964), and Warhol ("Double Mona Lisa", 1963); and pieces by contemporary artists such as Damien Hirst and Robin Rhode. He was involved in L.A.'s Ferus and Virginia Dwan galleries in the 1960s, and he was a longtime friend and supporter to New York dealer Tony Shafrazi. One of the first art works Hopper owned was an early print of Andy Warhol's Campbell's Soup Cans bought for US$75. Hopper also once owned Warhol's "Mao", which he shot one evening in a fit of paranoia, the two bullet holes possibly adding to the print's value. The print sold at Christie's, New York, for US$302,500 in January 2011. The proceeds of the two-day sale of some 300 pieces from Hopper's collection at Christie's went to his four children.