In the sixties and early seventies Zappa's band was called the »Mothers of Invention«. The members of the group had to obey to his instructions very strictly. Zappa didn't allow any compromise because he was very extreme especially in terms of music. This might be the reason for the progressive Zappa-sound. Some people said, that Zappa was the most intelligent asshole they ever met. In 1966, the »Freak Out« was released. It was the first »double-album« in rock history.