Born in 1937 in Castellon, Spain his family soon relocated to Mexico during the Spanish Civil War. Whilst in Mexico, Sergio received his education, eventually studying Architecture at the University of Mexico while also studying pantomime under the direction of Alexandro Jodorowsky. Always the avid cartoonist having discovered the craft in the third grade he contributed to school newspapers and anywhere else he could get his sketches printed and at age 17 began selling professionally to a wide array of Mexican publications. He maintained a weekly spot for over ten years in Mañana Magazine but in 1962 he made the decision to try to break into the American industry and so moved to New York City with only 20 dollars and his portfolio of work.