John Cage
John Cage is the 20th century conceptual artist who famously "composed" the piano piece titled 4' 33" (1952), which consists of the pianist(s) sitting at a piano and not playing for exactly four minutes and 33 seconds. The son of an inventor, Cage spent time in Europe as a young man, absorbing culture and studying with composer Arnold Schoenberg. He returned to the United States in the 1930s as a composer with an avant-garde approach, composing pieces for percussion groups and for what was called "prepared piano" -- a piano with various objects inserted between the strings for percussive effects. He taught briefly at the Chicago School of Design (1941-42) before moving to New York, where he continued to experiment and push the boundaries music, and embarked on a career of what he called "an exploration of non-intention." Cage used found objects and ambient sound, experimented with magnetic tape editing and splicing and used a variety of composing methods (including using the I Ching and star maps) to create compositions that were usually performed live instead of recorded. He became known outside the art world in the 1960s as an influence on pop art and rock music, and continued to lecture and compose until his death in 1992. Some consider Cage little more than a charlatan, but his idea that "everything we do is music" has undoubtedly influenced modern composers. Some of his other works include Imaginary Landscape #3 (1942), Variations I and II (1958) and Thirty Pieces for Five Orchestras (1981).
Extra credit: Some sources, including The New Oxford Companion to Music, give Cage's birthdate as 15 August 1912.
Related famous figures include radical thinkers Gertrude Stein, R. Buckminster Fuller and minimalist musician Brian Eno.