The 1968 album "" is regarded as the musical manifesto of the Tropicália movement. Although it was a collaborative project, the main creative forces behind the album were Caetano Veloso and Gilberto Gil. The album experimented with unusual time signatures and unorthodox song structures, and also mixed tradition with innovation. Politically, the album expressed criticism of the coup d'état of 1964. Key artists of the movement include Os Mutantes, Gilberto Gil, Gal Costa and Caetano Veloso. According to Maya Jaggi, "Gil was partly inspired by Jorge Ben Jor, a Rio musician on the fringes of the movement, who mixed urban samba and bossa nova with rhythm and blues, soul and funk."