Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
Coca-Cola
During the 1980s, Pepsi-Cola ran a series of television advertisements showing people participating in taste tests demonstrating that, according to the commercials, "fifty percent of the participants who said they preferred Coke "actually" chose the Pepsi." Statisticians pointed out the problematic nature of a 50/50 result: most likely, the taste tests showed that in blind tests, most people cannot tell the difference between Pepsi and Coke. Coca-Cola ran ads to combat Pepsi's ads in an incident sometimes referred to as the "cola wars"; one of Coke's ads compared the so-called Pepsi challenge to two chimpanzees deciding which tennis ball was furrier. Thereafter, Coca-Cola regained its leadership in the market.