It's not hyperbole to say that Astor Piazzolla is the single most important figure in the history of tango, a towering giant whose shadow looms large over everything that preceded and followed him. Piazzolla's place in Argentina's greatest cultural export is roughly equivalent to that of Duke Ellington in jazz -- the genius composer who took an earthy, sensual, even disreputable folk music and elevated it into a sophisticated form of high art. But even more than Ellington, Piazzolla was also a virtuosic performer with a near-unparalleled mastery of his chosen instrument, the bandoneon, a large button accordion noted for its unwieldy size and difficult fingering system. In Piazzolla's hands, tango was no longer strictly a dance music; his compositions borrowed from jazz and classical forms, creating a whole new harmonic and rhythmic vocabulary made for the concert hall more than the ballroom (which was dubbed "nuevo tango"). Some of his devices could be downright experimental -- he wasn't afraid of dissonance or abrupt shifts in tempo and meter, and he often composed segmented pieces with hugely contrasting moods that interrupted the normal flow and demanded the audience's concentration. The complexity and ambition of Piazzolla's oeuvre brought him enormous international acclaim, particularly in Europe and Latin America, but it also earned him the lasting enmity of many tango purists, who attacked him mercilessly for his supposed abandonment of tradition (and even helped drive him out of the country for several years). But Piazzolla always stuck to his guns, and remained tango's foremost emissary to the world at large up until his death in 1992.