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He started playing drums at the age of 13. By the time he was 15 years old he started playing drums with several bands in Athens. Later on he met Vangelis and Demis Roussos, they formed Aphrodite's Child. In 1967 they signed with Mercury Records in France and they release three albums: End of the world (which includes the song "Rain and Tears"), It's Five O'Clock and 666, the latter of which sold 20 million copies worldwide.
After Aphrodite's Child split up in 1972, Lucas began to compose his own music and released his first solo album, One Day with Polydor-France, selling 28.000 copies. In 1974 Lucas released another solo album, Pax Spray, that sold 45.000 copies.
Sideras was also active as a producer. In 1975 he produced the album Alba for Riccardo Cocciante which hit #1 in Italy’s charts. In 1979 he produced the album Love's Fool for Sigma Fay, selling 75.000 copies. In 1981 he produced the album Dead Line for Sigma Fay, which sold 52.000 copies. In 1984 he produced the single "You're the Drug in My Life" for Sigma Fay, sold 34.000 copies.
In 1977 Sideras formed the group Ypsilon with Lakis Vlavianos and Dimitris Katakouzinos. They released an album Morning Sunrise, which sold 75.000 copies and followed this in 1984 with Alien child, which sold 60.000 copies.
In 1987 he formed the blues-rock band Diesel with Sigma Fay and Yanis Drolapas. The band was together for ten years and appeared regularly as a live act and in jamming sessions but their sole release was the 1995 album Diesel. Whilst with the band Sideras also composed music for several documentaries and advertisements in his studio.
In 2005 he formed the blues-rock band Los-Tres with Simos Kokavesis and Bary Zealy and they have appeared live numerous times. In 2008 Sideras released a solo album Stay With Me which he composed arranged and produced in his studio. The album was strongly influenced by World music.