To an unknown hero whose memory we are supposed to celebrate (according to the subtitle). However, there's quite a lot of evidence in favor of Napoleon Bonaparte as the not-mentioned hero. It's almost sure that Beethoven had the French consul in mind when he wrote the symphony (1802/3). At the time he considered a trip to Paris and even pondered about moving to France forever. But then the picture changed. We all know the famous testimony of his friend and pupil Ries who brought him the news (spring 1804) that Bonaparte had declared himself an emperor, expecting that the Pope would be willing to crown him, which indeed happened. According to Ries Beethoven got very angry, went to his desk, gripped the score of the just finished symphony and tore the first page (on which he had written down the dedication) to pieces. Then he shouted that "now" Bonaparte would become a dictator and that he would trample down human rights. He surely was right... He renamed the symphony into "Eroica", but later on in a letter to the publisher he frankly admitted that the "true" name of the symphony was "Bonaparte." It's striking that he did not mention the name of the emperor-to-be (Napoleon), but Bonaparte, the name of the uncrowned consul. In 2007 Steblin offered a surprising view on the funeral march of the symphony: the mysterious dead person is... the Elector, Beethoven's mecenas of his youth.
See:
Solomon, Maynard. Beethoven. (London/New York, 1977).
Geck, Martin und P.Schleuning. 'Geschrieben auf Bonaparte'. (Hamburg, 1989).
Schleuning, Peter. Die Urauffuhrungsdatum von Beethovens 'Sinfonia Eroica'. In: Die Musikforschung (1991).
Brauneis, Walther. '...composta per festeggiare il sovvenire di un grand Uomo'. Beethovens 'Eroica' als Hommage des Fursten Joseph Maximilian von Lobkowitz fur Prinz Louis Ferdinand von Preussen In: Jahrbuch des Vereins fur Geschichte der Stadt Wien. (Wien, 1997).
Sipe, Thomas. Beethoven: Eroica Symphony. (Cambridge/New York/Melbourne, 1998).
Steblin, Rita. Who died? The funeral march in Beethoven's Eroica Symphony. In: The Musical Quarterly (2007).