Osvaldo Nicolás Ferraro Gutiérrez (7 September 1934 – 28 March 1977) better known as Waldo de los Ríos was an Argentine composer,[1] conductor and arranger.

De los Ríos was born in Buenos Aires into a musical family; his father was a musician and his mother a well known folk singer; he studied composition and arranging at the National Conservatory of Music under Alberto Ginastera, Teodoro Fuchs, and Lita Spena.

He arranged and conducted the Spanish entry for the Eurovision Song Contest 1971, "En un mundo nuevo" for Karina.

A victim of an acute depression while working on "Don Juan Tenorio", De los Ríos committed suicide in Madrid in 1977.

During late 60s and mid 70s he made several arrangements for many Spanish and international famous artists such as: Raphael, Mari Trini, Alberto Cortez, Facundo Cabral, Tony Landa, Jeanette Dimech, Miguel Ríos, Los Pekenikes, Maria Ostiz, Karina, Paloma San Basilio, Los Payos, etc.

On 10 March 2010 The Rush Limbaugh Show played an AM radio optimized mix of de los Ríos's version of Symphony No.