New Coke

1985-2004

The rivalry between Coca-Cola and Pepsi escalated in 1975 with »The Pepsi Challenge,« where consumers in blind taste tests preferred Pepsi over Coca-Cola. Coca-Cola responded by doing extensive market research that confirmed that consumers preferred a sweeter version of the original recipe. Coca-Cola changed its classic recipe in 1985 and launched what was called New Coke. Coca-Cola consumers were furious that the recipe had been changed. The original formula was rapidly re-introduced and rebranded as Coca- Cola Classic. There are many conspiracy theories about this. One is that Coca-Cola could not possibly have been so stupid and that really the whole ordeal was a sneaky way for the company to replace cane sugar with cheaper sweeteners. Or that it was a very advanced marketing ploy. 

Additional info:

This is such a huge and classic new product failure that there is very much information about it.

Wikipedia - Cola Wars. This is a good place to start

The Coca-Cola Company - The Story of One of the Most Memorable Marketing Blunders Ever

History.com - Great article and a very interesting documentary episode

Nytimes - New Coke Was a Debacle. It’s Coming Back. Blame ‘Stranger Things’

A informative video from CBS News: