is this the first muscle car?

Opinions vary quite a bit on the "first" muscle car. The '61 Impala SS gets plenty of votes to hold that honor, but the Chrysler 300 series "letter cars," which ran from 1955 to '65, and the 1964 Pontiac Le Mans GTO are contenders. No matter where it began, the American appreciation of under-the-hood muscle continues to this day, and with the return of the Challenger and the GTO to active production, not to mention the new G8, it looks like we may get to enjoy a new muscle era.