Nadezhda von Meck
In 1877 she came into contact with Tchaikovsky, although she never met him.  She asked him to compose some pieces for violin and piano to play at her home. Tchaikovsky knew she was a rich lady who paid well, so he quickly composed some music.  They wrote letters to one another, exchanged photographs of one another, but they came to an agreement that they would never meet.  She paid him 6,000 rubles a year.  This was a lot of money: about twenty times the salary of an ordinary government worker.  He was able to stop teaching at the Moscow Conservatory and spend his time composing.  Between 1877 and 1890 they wrote about 1,200 letters to one another.  Her encouragement was very important to him, and helped him to keep happy when he felt depressed.