When he founded the Nuclear Art movement in 1951 with Sergio Dangel, with whom he also published the Manifesto in 1952, Baj was painting vague, haunted swirls. In 1954 he began to evolve toward a form of expressionism, and participated in the activities of the Phases group. Baj decisively positioned himself with the surrealists in 1959, a period that saw the emergence in his work of a figure he called II Signor Olo, which he described as an "ultra-body," reduced as it was to a head and two legs. Baj’s ultra-bodies, first presented as creatures from outer space, soon developed a more specific identity—they became generals, at once sinister and farcical, studded with genuine medals, sometimes on their noses. Baj was a virtuoso of the collage-picture, and by assembling the most disparate materials—belts, mirrors, pieces of fabric and wallpaper—he made startling creatures appear against a background of tapestry or ticking. In his period-furniture style (1961), his figures were made from chests of drawers or wardrobes. Baj also illustrated Lucretius' De Natura Rerum and painted parodies of Picasso paintings (Les Demoiselles d'Avignon, 1969). He was later considered one of the exponents of the new narrative figuration, which inspired him to paint a 46-foot-long canvas, Les Funéralles de l’anarchiste PineIli (1970-1). Baj confirmed his return to painting in 1991, with an exhibition at the Galerie Beaubourg featuring paintings where the heads of men and animals were presented on their own, no longer owing their evocative power to a mosaic of affixed elements.
Born 1924 in Milan; died 2003 in Vergiate, Italy.