Coca-Cola Zero was launched in 2005 as a zero-calorie alternative designed to resemble Coca-Cola Classic.
The product was created for consumers who wanted the taste profile and branding cues of regular Coca-Cola without its sugar and calories. It was positioned differently from Diet Coke, whose flavor and marketing identity had been established decades earlier.
Coca-Cola Zero was later reformulated and renamed Coca-Cola Zero Sugar in many markets. That later name is why modern packaging may not match the original 2005 launch name. The question refers specifically to the product’s debut branding.
Coca-Cola Zero should also be distinguished from New Coke, the 1985 reformulation of the original cola. New Coke concerned a changed recipe, while Coca-Cola Zero was a separate zero-calorie product line.