Why is Beethoven's fifth piano concerto called 'the emperor'?

I have never heard or seen a definitive answer to this question. Beethoven himself never gave the concerto a name, though the piece is dedicated to Archduke Rudolf of Austria, one of Beethoven's patrons and students. read more

The Piano Concerto No. 5 in E ♭ major, Op. 73, by Ludwig van Beethoven, popularly known as the Emperor Concerto, was his last completed piano concerto. It was written between 1809 and 1811 in Vienna, and was dedicated to Archduke Rudolf, Beethoven's patron and pupil. read more

Emperor Concerto, byname of Piano Concerto No. 5 in E-flat Major, Op. 73, piano concerto by Ludwig van Beethoven known for its grandeur, bold melodies, and heroic spirit. The work was dedicated to Archduke Rudolf, who was a friend and student of the composer. read more