Task: Question Answering
Input (English): Passage: The infrequency of Tchaikovsky's musical successes, won with tremendous effort, exacerbated his lifelong sensitivity to criticism. Nikolai Rubinstein's private fits of rage critiquing his music, most famously attacking the First Piano Concerto, did not help matters. His popularity grew, however, as several first-rate artists became willing to perform his compositions. Hans von Bülow premiered the First Piano Concerto and championed other Tchaikovsky works both as pianist and conductor. Other artists included Adele Aus der Ohe, Max Erdmannsdörfer, Eduard Nápravník and Sergei Taneyev.
Another factor that helped Tchaikovsky's music become popular was a shift in attitude among Russian audiences. Whereas they had previously been satisfied with flashy virtuoso performances of technically demanding but musically lightweight compositions, they gradually began listening with increasing appreciation of the music itself. Tchaikovsky's works were performed frequently, with few delays between their composition and first performances; the publication from 1867 onward of his songs and great piano music for the home market also helped boost the composer's popularity.During the late 1860s, Tchaikovsky began to compose operas. His first, The Voyevoda, based on a play by Alexander Ostrovsky, premiered in 1869. The composer became dissatisfied with it, however, and, having re-used parts of it in later works, destroyed the manuscript. Undina followed in 1870. Only excerpts were performed and it, too, was destroyed. Between these projects, Tchaikovsky started to compose an opera called Mandragora, to a libretto by Sergei Rachinskii; the only music he completed was a short chorus of Flowers and Insects.The first Tchaikovsky opera to survive intact, The Oprichnik, premiered in 1874. During its composition, he lost Ostrovsky's part-finished libretto. Tchaikovsky, too embarrassed to ask for another copy, decided to write the libretto himself, modelling his dramatic technique on that of Eugène Scribe. Cui wrote a "characteristically savage press attack" on the opera. Mussorgsky, writing to Vladimir Stasov, disapproved of the opera as pandering to the public. Nevertheless, The Oprichnik continues to be performed from time to time in Russia.The last of the early operas, Vakula the Smith (Op.14), was composed in the second half of 1874. The libretto, based on Gogol's Christmas Eve, was to have been set to music by Alexander Serov. With Serov's death, the libretto was opened to a competition with a guarantee that the winning entry would be premiered by the Imperial Mariinsky Theatre. Tchaikovsky was declared the winner, but at the 1876 premiere, the opera enjoyed only a lukewarm reception. After Tchaikovsky's death, Rimsky-Korsakov wrote the opera Christmas Eve, based on the same story.Other works of this period include the Variations on a Rococo Theme for cello and orchestra, the Third and Fourth Symphonies, the ballet Swan Lake, and the opera Eugene Onegin. 
Question: What is the name of the person whose music Rubinstein would fly into private fits of rage critiquing?
Output (English): Tchaikovsky.