Wiki: "The name "Moonlight Sonata" comes from remarks made by the German music critic and poet Ludwig Rellstab. In 1832, five years after Beethoven's death, Rellstab likened the effect of the first movement to that of moonlight shining upon Lake Lucerne. Within ten years, the name "Moonlight Sonata" ("Mondscheinsonate" in German) was being used in German and English publications."
Also: "The first seven songs of Franz Schubert's Schwanengesang have words by Rellstab."
Also: "The first seven songs of Franz Schubert's Schwanengesang have words by Rellstab."