The first Mustang: the Mustang 1 concept of 1962.

The Avanti, later dubbed the Allegro, was a another early concept for what became the Mustang.

An early sketch for the Mustang, by designer Gale Halderman.

Ford briefly considered a four-door Mustang, an idea that, thankfully, never got beyond the prototype stage.

The 1967 Allegro II concept, which looks a bit like a second-gen Camaro mashed up with... well, we're not sure.

An early design sketch for the Mach I, which shows a decidedly Italian influence.

The Mach 1 concept shown at the Detroit Auto Show in 1967.

Ford hoped to capitalize on the success of the Mustang with a mid-engined replacement for the Shelby Cobra.

Ford shoulda built this one: the 1970 Mustang Milano. It's like a Pantera, but cooler.

This early prototype for the Mustang II is much prettier than the car Ford actually built.

A Mustang, as envisioned by Italians, for rally racing.

Rambo, a design study for the fourth-generation Mustang, was a bit burlier than the one called "Bruce Jenner."

The Mach III concept of 1992 provided a glimpse of the styling of the fourth-generation car.

An early design sketch of a futuristic, yet retro, fourth-generation Mustang.

Ford went way back to the future in this design sketch for the fifth-generation Mustang.