H.C. Robbins Landon, an American musicologist whose research helped to restore many of Haydn's works to the active repertory after more than a century of neglect, and whose popular books about Mozart countered many popular myths about that composer's life, died on Friday at Rabastens, near Toulouse, France. He was 83. Rabastens town officials confirmed his death but did not specify the cause. Though a serious and prolific scholar, Landon also had a knack for making musicology seem exciting to the general public. He was a founder (or 'instigator,' as he put it) of the Haydn Society, which started in Boston in 1949 and later moved its center of activities to Vienna. The society produced a series of recordings including previously unrecorded Haydn symphonies and Masses as well as the first recordings of Mozart's 'Idomeneo' and Mass in C minor. In the 1950s Landon provided commentary for BBC orchestral broadcasts, and in the 1960s he collaborated with the television producer Humphrey Burton on a series of BBC television documentaries about Italian Baroque composers -- a subject he returned to in 'Maestro,' a 1990 series he produced with John Julius Norwich for Channel 4 in Britain (and which also yielded a book, 'Five Centuries of Music in Venice,' in 1991). He published a useful introduction to the life and music of Handel, 'Handel and His World' (1984), as well as five books about Mozart, published between 1988 and 1995. In '1791: Mozart's Last Year,' he dismissed the notions, popularized in Peter Shaffer's 1979 play, 'Amadeus' (and the 1984 movie), that Mozart had been poisoned, that he had a fraught relationship with the composer Antonio Salieri, and that his Requiem was commissioned by a mysterious stranger. But Landon's true life's work was bringing Haydn and his music fully into the spotlight. He said he decided to undertake that mission in 1939, when he was a 13-year-old at a boarding school in North Carolina, fascinated by concert broadcasts from New York. After hearing a few Haydn symphonies -- at the time only a handful were regularly performed -- he told a teacher, Mathias Cooper, that he wanted to study music. In a 2008 interview with the early-music magazine Goldberg, Landon said it was Cooper who suggested that he specialize in Haydn. 'So I asked him, 'Why Haydn?' and he told me that Haydn needed a Gesamtausgabe. I said, 'What's a Gesamtausgabe?' He explained that it was a complete edition of a composer's works and everyone has one: Mozart, Beethoven, Brahms, even Buxtehude. But not Haydn.' Howard Chandler Robbins Landon was born in Boston on March 6, 1926, and studied composition with Harl McDonald at Swarthmore College before moving to Boston University, where one of his principal teachers was Karl Geiringer. He completed his bachelor's degree in 1947, but quickly realized that if he intended to specialize in Haydn he should be based in Europe. Traveling through England, the Netherlands, Austria and France, he worked as a correspondent for Musical America and other American publications and became a musical correspondent for The Times of London. That position made it possible for Landon to make his way to Hungary, where Haydn had been employed by the Esterhazys, and where many of his manuscripts were archived. He was assisted in his research by his first wife, Christa Landon, a harpsichordist. She died in a plane crash in 1977. Landon later married Else Radant, a historian; they separated in 1994. Radant survives him, as does Marie-Noelle Raynal-Bechetoille, his longtime companion. Landon began by editing critical editions of Haydn's works in the '40s, and in 1955 he published 'The Symphonies of Joseph Haydn,' which established the works' chronology. He also published critical editions of Haydn's Masses and operas, many of which had not been performed in modern times. In many cases Landon's efforts involved finding pieces of a work and assembling them. 'There were many symphonies that even if you wanted to do them, you couldn't because there was no score and no parts,' he said in 2008. 'Symphony No.51, for example, could not be performed. So my task was to start preparing editions, and now of course they are all issued and they sell very well.' The zenith of his work on the composer is 'Haydn: Chronicle and Works,' published in five volumes, between 1976 and 1980. Landon's enthusiasm for Haydn could lead him astray. In 1993 he and the pianist-musicologists Paul and Eva Badura-Skoda announced what they said was a major find: a set of six lost Haydn piano sonatas. Landon declared them authentic, although he had seen only photocopies. When further study raised questions about the provenance of the pieces -- which were eventually proven to be the work of a modern German composer -- Landon changed his mind, agreeing with other musicologists that the set was, after all, 'a rather sinister forgery.' Landon held teaching positions at Queens College, New York; the University of California, Davis; and the University of Wales, Cardiff. Among his final books were 'Vivaldi: Voice of the Baroque' (1993) and an autobiography, 'Horns in High C: A Memoir of Musical Discoveries and Adventures' (1998). 