Vandor was born in Bovril, Entre Ríos Province, to a Dutch father and a French mother, in 1923. He enlisted in the Argentine Navy in 1941, and later became a non-commissioned officer aboard the minesweeper ARA "Comodoro Py". He left the Navy in 1947, however, and joined the new Philips factory in the Saavedra neighborhood of Buenos Aires. There, he met his future wife, and gained a reputation for strategic thinking that earned him the nickname of "El Lobo" (the Wolf). He became the steward of the Phillips factory UOM local and in 1954, led a strike for better pay at the facility. Its success made him prominent in the UOM (the steelworkers' union within the CGT, the paramount trade union in Argentina), but led to his arrest following a 1955 military coup that overthrew the populist administration of Juan Perón.