The first generation of Ford Mustang was introduced in 1964. Due to the Mustang's early release in 1964, there is an unofficial 1964 1/2 version, although officially the first Mustangs were 1965 models. The first generation Mustang is one of the automotive world's most well known and important models, helping to launch a new segment (pony car), and creating a range of iconic variants such as the Boss 302, Boss 429, Mach 1, and Boss 351, as well as the legendary Shelby Mustang. First generation cars were offered as rear wheel drive convertibles, fastbacks, or hardtops, and were available with a wide range of inline six and V8 engines. This initial generation of Mustang saw regular styling and mechanical updates every two years, resulting in four evolutions: 1965-1966, 1967-1968, 1969-1970, and 1971-1973. At the end of First Generation Mustang production, it was replaced by the Second Generation Ford Mustang.