Note that Tchaikovsky wrote ten operas--Queen of Spades, Eugene Onyegin,
and Iolanta come to mind.

Aaron J. Rabushka
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 [He wrote eleven complete operas.  From the Tchaikovsky works list
 by Brett Langston accessible via Classical Net:

   The Voyevoda, Op. 3 (1867-68)
   Undina (1869)
   The Oprichnik (1870-72)
   Vakula the Smith, Op. 14 (1874)
   Eugene Onegin, Op. 24 (1877-78)
   The Maid of Orleans (1878-79)
   Mazepa (1881-83)
   Cherevichki (1885)
   The Enchantress (1885-87)
   The Queen of Spades, Op. 68 (1890)
   Iolanta, Op. 69 (1891)

 There's also a description of each and an interesting list of opera
 projects he considered or started.  -Dave]