Simón Narciso Díaz Márquez (August 8, 1928 – February 19, 2014), also known as tío Simón, was a Venezuelan singer, actor, TV host, comedian, and Grammy Award-winning composer of Venezuelan music. Some of his most popular songs include Caballo viejo, Tonada de luna llena and La vaca Mariposa.

Díaz endeavored to recover the folklore and musical traditions of the Venezuelan llanos (plains). This style of music has since been performed by artists such as Argentina's Mercedes Sosa, Brazil's Caetano Veloso, Spain's Joan Manuel Serrat, Peru's Susana Baca, Puerto Rico's Danny Rivera, and Venezuelans Franco De Vita, Soledad Bravo, Juan Carlos Salazar, Carlos Baute and José Luis Rodríguez, among others. Many of Díaz's works have been adapted by symphonies and choral ensembles throughout Venezuela, as well as being incorporated into the orchestral and choral arrangements of conductors and composers of academic music.

Artists from other disciplines have also utilized Díaz's work. For example, German choreographer Pina Bausch included some of Díaz's songs in her work Nur Du. Film director Pedro Almodóvar included Díaz's song "Tonada de luna llena" as part of the soundtrack for his film The Flower of My Secret, sung by the Brazilian artist Caetano Veloso.