Belu Zilber (born Herbert Zilber; October 14, 1901–February 1978) was a Romanian communist activist.

Born into a Jewish family in Târgu Frumos, Iași County,^[1] he adhered to the Bolshevik movement while still an adolescent. Because he participated in the typographers' demonstration of December 13, 1918, he was expelled from every educational institution in his native country by the authorities of the Kingdom of Romania.^[1][2] He continued his high school education in Paris and began but did not complete studies at the polytechnic division of the University of Grenoble. He returned to Romania in 1922 and was hired as an expert at the War Ministry.^[2] He was recruited as a Soviet spy in Vienna in 1928; arrested in Romania in December 1930, he agreed to become an informant for the Siguranța secret police.^[1] At his trial for espionage on the Soviets' behalf, he was initially sentenced to five years at hard labor.^[3] After spending time at Doftana Prison and at labor camps in Caransebeș and Târgu Jiu (where he got close to Gheorghe Gheorghiu-Dej's group),^[4] he was retried and acquitted in 1932.^[3]

That year, he began working at an institute led by Virgil Madgearu, where he remained until 1947.^[1][2] During the rest of the decade, Zilber, characterized as "cultured, voluble and ubiquitous", and known in the cultural circles of Bucharest, led an underground life as a member of the banned Romanian Communist Party working to destroy "bourgeois democracy", an informer and a spy, but also lived the seemingly normal life of a bourgeois desirous of prosperity.^[2] Following the Coup of August 1944, when the Communist Party was made legal, he became the closest collaborator of his friend Lucrețiu Pătrășcanu, who became Justice Minister.^[5] He became a professor of political economy at the University of Bucharest and received a Ph.D. in philosophy. During that time, he married Nuțu Fuxman (Ana Naum). From August to November 1946 he was in Paris as part of the Romanian delegation to the Paris Peace Conference. In May 1947 he was excluded from the Communist Party, and in the fall of that year he was forbidden from teaching at the university, on orders from the Education Minister, Ștefan Voitec.^[4] Zilber was arrested in 1948, together with Pătrășcanu, and imprisoned following a show trial. He was released in 1964.^[2][6][7] He died in 1978. Following incineration at the Cenușa crematorium, his ashes were taken to Cișmigiu Gardens, where they were scattered under a bush near the bust of George Panu, among the magnolias he often admired.^[6] His memoirs appeared posthumously in 1997, some years after the 1989 fall of the regime.^[3]