Charles Mingus Jr. (April 22, 1922 – January 5, 1979) was an American jazz upright bassist, composer, bandleader, pianist, and author. A major proponent of collective improvisation, he is considered one of the greatest jazz musicians and composers in history, with a career spanning three decades and collaborations with other jazz greats such as Duke Ellington, Charlie Parker, Max Roach, and Eric Dolphy. Mingus's work ranged from advanced bebop and avant-garde jazz with small and midsize ensembles to pioneering the post-bop style on seminal recordings like Pithecanthropus Erectus (1956) and Mingus Ah Um (1959) and progressive big band experiments such as The Black Saint and the Sinner Lady (1963). Mingus's compositions continue to be played by contemporary musicians ranging from the repertory bands Mingus Big Band, Mingus Dynasty, and Mingus Orchestra to high school students who play the charts and compete in the Charles Mingus High School Competition. In 1993, the Library of Congress acquired Mingus's collected papers—including scores, sound recordings, correspondence and photos—in what it called "the most important acquisition of a manuscript collection relating to jazz in the Library's history".