Legend says that ouzo was initially created by a group of 14th century Monks who lived in a monastery on the holy mountain of Athos. Ouzo really took off in the 19th century following Greek independence. Much of the product was and still is on the island of Lesbos, which also claims were the spirit was invented. It really took off in the early 20th century when absinthe went out of favour and ouzo was seen as a replacement without the worm wood.
The production of ouzo starts with it being at 96% ABV being contained in copper stills. To the alcohol they add anise and then other ingredient depending on the type of ouzo they want to create. Other ingredients are Star anise, cinnamon, coriander and cloves. The exact flavouring is not known as it is a closely guarded secret. Makers of 100% would simply add water at this stage to bring the ABV level down, but others will add different ingredients such as sugar to the mix. The final abv is between 40-50% with the minimum being 37.5%
Ouzo is traditionally served with water and over ice, to be sipped while eating a mezedes, which is a combination of appetisers. Or it is drunk before a meal and served extra chilled with no ice or water, sometimes so chilled that ice crystals begin to form in the spirit.