Aznar studied classical guitar, piano, electric and acoustic bass, percussion, and composition in Buenos Aires and at the Berklee College of Music in Boston, Massachusetts. He founded the group Serú Girán in 1978, one of the most popular and influential ensembles in Latin American popular music. Serú Girán disbanded in 1982, but reunited in 1992, producing a platinum studio album and gathering the largest audience, up to that point, for a concert tour in Argentina. Aznar joined the Pat Metheny Group in 1983 as multi-instrumentalist and singer after Pat Metheny heard a tape of his home recordings. The group featuring Aznar in the lineup toured the world extensively and recorded three Grammy-winning albums: First Circle, Letter from Home, and The Road to You, as well as the soundtrack to the film The Falcon and the Snowman. Aznar's second solo album, Contemplación, featured the accompaniment of several members of the Pat Metheny Group. As a member of that group, Aznar played guitar, saxophone, both untuned and tuned percussion (including steel drums), and melodica, in addition to singing and whistling. He also wrote or co-wrote several songs included on Pat Metheny Group albums.
Aznar released two records as a duo with Charly García: Tango in 1986 and Tango 4 in 1991 -- both of them went platinum. The latter also won the ACE Award of the Argentine Association of Entertainment Critics for Best Rock Album of that year. He also recorded with ethnomusicologist and researcher Leda Valladares on Grito en el Cielo, an anthology of Andean traditional folk songs. He wrote the scores to several films, winning the SADAIC Award (Argentine Composers Association) and three Silver Condors (Film Critics Association of Argentina) for Best Film Score. Aznar has also composed music for ballet, theatrical pieces, art exhibitions, multi-media events, and art videos, as well as a Concerto for String Orchestra and Synthesizers, commissioned by the Mayo Chamber Orchestra. In 1992, he published a poetry book, Pruebas de Fuego. He also composed and recorded duets with singers Mercedes Sosa and Caetano Veloso in 1993 for an album sponsored by UNICEF to advance awareness of Children's Rights. Aznar has released six solo albums, three soundtrack albums, and lent his considerable talents to over 40 albums with other artists. ~ Tim Griggs, Rovi