Marathon Swimmers lead the way in endurance feats. Captain Matthew Webb will be forever remembered as the first person to swim unaided across the English Channel and hence complete the first modern day marathon. On 25 August 1875 Capt. Webb zig zagged his was across the channel (covering total of 39 miles) to complete the swim to France in a little under 22 hours to claim his place in history.
OK, the very first marathon atlhlete was of course, legendary runner Pheidippides, running to Athens with the news of a military victory in the Battle of Marathon, only to die at the finish line. The year was 490BC. Fast forward a few years and it was not until De Coubertain's rebirth of the Olympic movement that the next running marathon was held, again in Athens in 1896 for the inaugural Modern Olympic Games.
So, despite marathons being long associated with running, arguably the first modern day marathoner was Capt. Webb. Decades ahead of his time and ahead of the sport of athletics with his marathon swim across the channel.