Greek Psychedelic space-rock band Aphrodite's Child began to record "666" late in 1970: a musical adaptation of the biblical Book of Revelation. Koulouris, having finished his Greek army duty rejoined the band. However, relations between all the band members were not good at the time, and continued to worsen during the album's creation.
Essentially, 666 was Vangelis' concept, created with an outside lyricist, Costas Ferris. The music that Vangelis was creating for 666 was much more psychedelic and progressive rock oriented than anything the band had done before.This did not sit well with the other band members, who wished to continue in the pop direction that had brought them success.Furthermore, Roussos was being groomed for a solo career, and recorded his first solo single "We Shall Dance" (with Sideras on drums), and his first solo album On the Greek Side of My Mind, whereas Vangelis recorded the score forL'Apocalypse des animaux and worked on a single with his girlfriend Vilma Ladopoulou, performing with Koulouris using the pseudonym 'Alpha Beta'.
By the time the double album 666 finally was released in June 1972, and having sold over 20 million albums,the band had already split.Both Vangelis and Roussos pursued successful solo careers, Roussos as a pop singer and Vangelis in electronic music. Koulouris worked with both on occasion. Sideras pursued a less successful solo career, releasing an album and the single "Rising Sun" after the break-up.