Although the 1964 Pontiac GTO gets all the credit, the 1957 Rambler Rebel was the first muscle car. In 1957 the Nash and Hudson marques were in their last year and the company was uniting under the Rambler name. American Motors president George Romney wanted to make a big splash, so he dropped the newly developed 327 into a relatively light weight four-door hardtop. At that time, none of the Big Three had a car as small as the intermediate-sized Rambler.
The fun only lasted one year, as the car did not catch on with the general public. The standard engine in 1958 was the 250 V8 and Rebel became an upmarket trim level. The nameplate was dropped after 1960. All Rebels were four-door hardtops, maybe it would have succeeded as a coupe. They weren't the prettiest cars in the pageant either.