‘Defining Moment’ is the story of John O’Regan, a forty one year old Irish ultra runner. A fascinating case of one person against the elements in Antarctica, the Arctic, Sahara Desert, Yukon, Peru, Greece and Ireland. What are the ingredients that make an ultra runner go through such grueling mental and physical pain? How is an ultra runner different from a marathon runner? This intriguing story reveals what makes him tick using the background story of his participation in the 2010 2500Th anniversary ‘Spartathlon’. Four hundred and fifty of the worlds top ultra runners registered for the 246km non-stop race from Athens to Sparta. 351 arrived at the start-line, but just 128 crossed the finishing line within the 36 hour limit.