Francesc Duran Reynals (1899–1958), born in Barcelona is a significant figure in virology, with the proposal of viral theory of cancer in the late 1920s, challenging existing beliefs about the non-contagious nature of cancer. He gained recognition for discovering the “Duran Reynals factor,” later identified as the enzyme hyaluronidase. Although his viral theory faced skepticism, Duran Reynals produced experimental evidence showing links between viruses and cancer. He mentored notable virologists, including Jordi Casals-Ariet and Jordi Folch-Pi, who made significant contributions to the field. His work remains influential, highlighting the viral origins of certain cancers.