There aren't many sporting events that I can think of that are based on a story from a ancient Greco war and named after a battle. Pheidippides was, of course, a messenger for the Athenian army. The story goes that after the Athenians were victorious over the Persians at the battle of Marathon, Pheidippides ran the 26 miles back to Athens to announce the victory. He made it back, stated "we have won", and died on the spot.
Not exactly a story that one would think would lead thousands of people every year around the world to try and equal his feat. I did a little reading on the internets - and the factual history around his run is a little shaky. But, more historically firm is the fact that he ran to Sparta to request help in battling the Persians before the battle of Marathon. To reach the Spartans and get back to the battle he ran 150 miles in two days BEFORE the famous 26 miles. No wonder he died - he didn't taper properly.