Vertov, Eisenstein and Pudovkin, all personal influences, were invited by Ivens to speak at his Amsterdam film-club. He met Krull while working in Berlin, and Ruttmann — even more influential — soon after. Buñuel got papers for him to shoot an anti-fascist film in Spain, with Hemingway and Dos Passos. Pudovkin invited him to a lecture-tour in the USSR: Eisenstein put him up. Storck, Eisler, Prévert, Marker and Thomson all collaborated with him; Chaplin, Flaherty, Capra, Dovzhenko and Losey were among his friends. Robeson and he engaged in a long-distance collaboration while both were black-listed by the U.S.