Actually, I think the original “muscle car” was either the Chevy Bel Air SS or Impala SS 409ci or the Ford Galaxie 390ci. Can’t remember which, but the Beach Boys song immortalized the 409, even though the 390 was available first. It was around 1961 that the “muscle car” era began.
However, those were full size performance cars and some consider the definition of “muscle car” as being the intermediate size that came out around 1964. So, pick your definition.
“Actually, I think the original “muscle car” was either the Chevy Bel Air SS or Impala SS 409ci or the Ford Galaxie 390ci. “
I think the first car intended to be a muscle car was the GTO. The history channel did something on muscle cars that was pretty good, they picked the GTO because it was the first car to be full sized, but lightened, with a big motor.
You could debate the point though, history channel isn’t the ultimate authority.