As a young artist Bull was mentored by the noted Western artist, Charles M. Russell.
Bull claimed to have photographed Lon Chaney made up as Jesus Crist, but the portrait has been lost.
According to a 1941 syndicated column by John Chapman, Bull was identified as Greta Garbo's preferred portrait photographer. He would reportedly take an average of 200 stills of Garbo over the course of shooting a film.