Arnaldo Dias Baptista (b. July 6, 1948 in São Paulo) is a Brazilian rock musician and composer. Born from a lyric singer father and a pianist mother, Arnaldo studied classic piano from 1955 to 1959, double bass from 1962 to 1963, and acoustic guitar from 1963 to 1965. In 1966 he formed the influential Os Mutantes band with his brother Sérgio Dias and Rita Lee, where he played bass, keyboards and sang. Os Mutantes played a key role in the Tropicalismo movement.