For many years it was believed that Beethoven's Piano Sonata No 21 in C was named after one of his patrons. It is true that Beethoven did dedicate the work to Count Ferdinand Ernst Gabriel von Waldstein of Vienna, but it acquired its popular name for quite a different reason.
The composer had a very dear friend called Mr Waldstein. They had both studied counterpoint with Johann Albrechtsberger in 1795 and kept up a relationship by correspondence for some years. By 1804, however, Beethoven had started to make a name for himself while his friend's career had faltered, and, perhaps through jealousy, Waldstein had stopped replying to Beethoven's letters. This hurt Beethoven deeply, and in the sonata he wrote in that year he included a coded message in the first movement, intended as a gentle reminder.
It was a plaintive melody, GFEDC, DEFGF, and it meant "Oh, Mr Waldstein, why don't you ring me?"
Sadly, there is no record of him ever getting a response.