Introduced as it was smack in the middle of a model year, the first Mustang was the “1964-1/2”. Ever wonder where the term “pony car” came from? The original Mustang began as an industry-wide sensation in 1964, when two sporty new performance models were initially offered, a classy coupe and a convertible. There were 28,833 topless Mustangs built before the “actual” 1965 production began.