So for people who don't want to go to the link the story is:
Blizzard had a contest before Diablo was released to have someones name inputted into the diablo franchise. This kids dad being a blizzard fan decided to send in his son's name (due to the fact that his name is epic) and actually ended up winning. Therefore Deckard Cain is a real person and is actually only about 16 years old.