St. Stephen was a little known saint who achieved eternal fame by being the first Christian to be martyred for his faith, and he met his death by stoning.
The holiday may date from as early as the Middle Ages, but the exact origin is not known. It may have begun with the Lords and Ladies of England, who gave Christmas boxes/gifts to their servants on December 26, or maybe by priests, who opened the church's alms (charity boxes), and distributed the contents to the poor and needy.
A day to visit other relations, and to have a rest from the day before, to play fun games. Some families, buy a new game each year, but still bring out the old favourites :-)
For some it is good to have the 2 days, as on one of the days you can visit with your parents, and the other day your inlaws :-)
St Stephen is the patron saint of horses, so Boxing Day became associated with horse-racing and hunting. Other sports are also held on this day like football and rugby. And its full of EPL action for these week. Football, football, and nothing but football.
Happy Boxing Day, and I hope you all have a wonderful holiday ahead and welcoming a new year "2006".