Apostolos Sideris was born in 1978 in Athens, where he had his first musical training, playing the classical flute. By the time he was 15 he had switched to the electric bass and he was soon playing with various rock bands.

By the time he was 18, his focus was directed towards Jazz music, something that lead him make the move and go to Boston, in order to attend Berklee, where he picked up the upright bass as his main instrument. After a period in Boston, he moved to New York and earned his Master's degree in Performance at CUNY, while being instructed by bass virtuoso, John Patitucci. Since then he has been freelancing around the States as well as abroad.

He has performed with a wide array of musicians ranging from jazz masters such as drummer Clarence Penn, to world music sensation Savina Yannatou and Syrian vocal master Youssef Khasab. In addition to being a performer, he is a part-time composer, having written in diffrerent styles, ranging from Jazz to Middle Eastern and Latin influenced music. He is currently residing in Istanbul.

His first personal album "Σummation" was released in 2019.