Tchaikovsky was arguably the greatest Russian composer of all time, and one of the greatest composers in history. Whether or not you realize it, you are probably quite familiar with many of his melodies: famous themes from ballets like Swan Lake, the Nutcracker, and Sleeping Beauty, for example, or the incredible finale of his 1812 Overture (the one that features live cannons). Going deeper into his oeuvre — symphonies, concerti, operas, and other pieces — many of his themes are instantly recognizable.
He was a hero of Russia. When news of his death reached the Tsar, he immediately offered to pay for the funeral. 60,000 people applied for tickets to Tchaikovsky's funeral (capacity was only 8,000) and many more lined the streets of St. Petersburg to pay respects to the procession.
But Tchaikovsky was a gay man living in a society that hated homosexuals. Tchaikovsky himself struggled with his orientation, attempting a marriage and then trying to kill himself by jumping into the cold Moscow River two weeks after the wedding. The marriage ended in six weeks.
The official cause of Tchaikovsky's death was cholera. There were outbreaks all over Russia at the time, and people were warned to boil their water before drinking it or even washing with it. According to reports, he asked for a glass of water in a restaurant and, informed they had no boiled water available, requested it unboiled. Two weeks later he was dead.
Even at the time there were doubts: a number of people noticed that his illness, treatment, and the handling of his body did not quite match the putative cause. In the 1970s a very different account was published, a story that had been kept secret for 80 years. According to this account, he was threatened by a secret "court of honour" with terrible reprisals, and was advised to kill himself as punishment for his homosexuality. Apparently he had fallen in love with his nephew, and the network of school alumni felt that any exposure would result in disgrace for the whole school. Here is biographer David Brown's version:
"The incident took place in the autumn of 1893. Tchaikovsky was threatened with terrible misfortune. Duke Stenbok-Fermor, disturbed by the attention which the composer was paying to his young nephew, wrote a letter of accusation to the Tsar and handed the letter to Jacobi. Through exposure Tchaikovsky was threatened with the loss of all his rights, with exile to Siberia, with inevitable disgrace. Exposure would also bring disgrace upon the School of Jurisprudence and upon all the old boys of the school, Tchaikovsky's fellow students. To avoid publicity Jacobi decided upon the following. He invited all Tchaikovsky's former schoolmates [he could trace in St. Petersburg], and set up a court of honour which included himself. Altogether there were eight people present. Elizveta Karlovna sat with her needlework in her usual place alongside her husband's study. From time to time from within she could hear voices, sometimes loud and agitated, sometimes dropping apparently to a whisper. This went on for a very long time, almost five hours. Then Tchaikovsky came headlong out of the study. He was almost running, he was unsteady, and he went out without saying a word. He was very white and agitated. All the others stayed a long time in the study talking quietly. When they had gone Jacobi told his wife, having made her swear absolute silence, what they had decided about the Stenbok-Fermor letter to the Tsar. Jacobi could not withhold it. And so the old boys [of the school] had come to a decision by which Tchaikovsky had promised to kill himself. A day or two later news of the composer's mortal illness was circulating in St. Petersburg."
As it happens his symptoms match arsenic poisoning much more closely than cholera. The day after the "glass of water" his brother found him in bed suffering from diarrhea and stomach pains. Tchaikovsky refused to call a doctor, and tried to carry on with his day, taking cod liver oil in an attempt to ease his stomach. Within days he was much worse, and a doctor diagnosed him with cholera. The mortality rate for cholera at that time was more than 40%, but he seemed to get better, then he would get worse again with more pains and cramps. Eventually his kidneys failed, a priest was called, and he died at 3am on November 6, 1893.
The movie, V for Vendetta, used the finale to the 1812 Overture to great effect. The Adagio from the Sixth Symphony is one of the most beautiful pieces of romantic music ever written: enjoy a rehearsal of it here.
Sources: Wikipedia article on Tchaikovsky, Wikipedia article on his death, Brown, David, Tchaikovsky: The Man and His Music (New York: Pegasus Books, 2007)