John Cage (1912-1992) was an American composer, artist, and all-around revolutionary figure in the birth of the American avant-garde art movement. One of Cage's trademark ideas, in terms of music and composition, was shifting the artistic focus away from the artist's psyche and and more towards their environment and surroundings.
Perhaps Cage's most famous piece, and certainly what first drew me to him, is the 1952 piece 4'33", which relies on complete silence of the instruments themselves, forcing listeners to instead focus on the sounds of the environment around them.
This piece is widely considered to be the proper beginning of noise music. Cage is also credited with creating the idea of 'prepared' instruments - stringed instruments altered by placing objects above, below, or entangled within the strings. The trademark instrument of this type, pioneered by Cage, is the prepared piano. Another notable instrument altered in this way is the prepared guitar.
Cage's work in the fields of art and music span much further than what's appropriate for the length of this post. He was a true trailblazer in terms of experimentation in music, and his affinity for the strange is what keeps people like me coming back to read up on him.
For more information on John Cage, click here.