On May 9, 1781, Wolfgang Amadeus Mozart — twenty-five, freshly arrived in Vienna in the service of Hieronymus Colloredo, the Archbishop of Salzburg — was literally kicked down a staircase by Colloredo's steward Count Arco after weeks of petitions to be released from service. The Salzburg years were over. Mozart spent the next decade in Vienna as one of the first major composers to attempt a freelance career — no court, no church appointment, dependent on subscription concerts, commissions, and aristocratic patronage. He died in December 1791, thirty-five years old, eight bars into the Lacrimosa of the Requiem. In the decade between those two dates he produced the three great Da Ponte operas, the late symphonies, seventeen Vienna piano concertos, the late string quintets, and the Requiem he did not live to finish — the densest concentration of canonical work in the Western tradition.
Mozart's mature synthesis fused three streams: Italian opera in the opera buffa tradition he had absorbed since childhood tours; German counterpoint studied through Baron van Swieten's Sunday Bach-and-Handel reading sessions starting in 1782 — Mozart's late style is unimaginable without that rediscovery; and the galant idiom inherited from J. C. Bach, Haydn, and the Mannheim school. The three Da Ponte operas — Le nozze di Figaro (1786), Don Giovanni (1787), Così fan tutte (1790) — established opera as serious dramatic art with fully-individuated characters, ensemble finales that develop plot rather than freezing it, and an orchestral commentary that became Wagner's later inheritance. Die Zauberflöte (1791) added the German Singspiel tradition. The seventeen Vienna piano concertos (K. 449–595, 1784–1791) effectively created the form as it would be used through Beethoven, Brahms, and Rachmaninoff — soloist and orchestra in genuine dramatic dialogue rather than the older accompaniment relationship. The late symphonies — No. 39 in E-flat, No. 40 in G minor (chromatic, almost agitated; the opening line a near-modernist falling chromatic figure), No. 41 in C Jupiter — were completed in summer 1788 in a single six-week burst, apparently without a planned performance. The string quintets (G minor K. 516; C major K. 515) are routinely placed beside Beethoven's late quartets as the summit of the chamber-music repertoire. The unfinished Requiem in D minor (K. 626) was completed after Mozart's death by his pupil Franz Xaver Süssmayr from the composer's sketches and is the work whose authorship boundary scholars still debate.
Mozart's reputation has had three distinct phases. The nineteenth century received him as a graceful Classical predecessor to Beethoven — a view Eduard Hanslick and others canonized. Alfred Einstein's 1945 biography re-established the dramatic and emotional depth the previous century had bracketed. Peter Shaffer's 1979 play Amadeus and the 1984 Miloš Forman film, while historically loose (the Salieri rivalry is largely fiction), brought Mozart to a vastly larger audience. The Köchel catalogue (Ludwig von Köchel, 1862, now in its eighth edition) numbers his works chronologically by K.-numbers. The Neue Mozart-Ausgabe (Bärenreiter, 1956–2007) is the modern scholarly edition. The historically-informed-performance movement (Nikolaus Harnoncourt, Christopher Hogwood, John Eliot Gardiner) has reshaped how the music sounds since the 1980s. The 1993 Mozart effect claim — that listening to Mozart raises IQ — was a small, narrowly-defined laboratory finding spun far beyond what it could support; the underlying claim has not replicated. Mozart remains the second-most-recorded composer in history after Bach.