Zelmar Casco was the nephew of Horacio Casco, president of the Club de Gimnasia y Esgrima La Plata from 1920 to 1925 and a fencer in four events at the 1924 Paris Olympics. Zelmar followed in his father’s footsteps and became one of Argentina’s premier fencers of the 1960s. The peak of his career came when he was selected to represent his country at the 1964 Tokyo Games in the épée, but he was eliminated in the opening rounds of both the individual and team competitions, the latter alongside Félix Galimi, Jesús Taboada, and Francisco Serp.