Waldo de los Rios (?-28 March 1977) was an Argentinian composer and arranger.
He was a native of Buenos Aires.
Waldo de los Rios is best-remembered for his ability to transform the classics of European classical music into pop music. He was best known for a 1971 update of Mozart's "Symphony No. 40." De los Rios' compositions were heard in the 1967 film Pampa Salvaje, for which he received a prestigious award from the Argentine Cinemagraphic Association.
His record Mozart in the Seventies rearranged famous Mozart pieces in a contemporary style, with a large percussion section. Several tracks from it were used as theme tunes to BBC programmes of that era.
De Los Rios committed suicicde in 1977.