Although there were plenty of cars before it that were considered fast, the 1964 Pontiac GTO may has been considered the first authentic muscle car. It maybe called the first but that was not enough to guarantee its continuous production. The Pontiac GTO was produced from 1964 to 1974 and it was revived for the 2004 model year. Although there was no convertible body style in this new model, there was a suitable rear-drive 2-door coupe. It was arguably a better muscle car than the 1964 but it sold poorly. Muscle car buyers had changed. In 1964 a plain Jane with a big engine was enough, but by the mid-90s more flash was required.
If you are looking for the most famous muscle car that goes 0 to 60 in 6.5 seconds, the 1966 Pontiac GTO is your best bet. When it was first introduced it immediately became a bestseller. Pontiac had produced a new masterpiece and it continues to be in high demand among car enthusiasts. From there the GTO continued to grow larger and faster until the early 70s when the legendary GTO emblems were applied to several different body styles with less than ground pounding power.