Arguably one of the most iconic automobiles ever built in the United States, the Ford Mustang->ke428 is already 50 years old and carries with it a rich heritage. If Ford would had not developed the Mustang and crafted the pony car concept, famed vehicles such as Chevrolet Camaro->ke248, Dodge Challenger->ke249 and Plymouth Cuda->ke1486 would have probably never existed. Sure, the `Cuda predated the Mustang, but the Mustang truly built the segment.

Of course, we can't claim that the muscle car->ke507 phenomenon wouldn't have gained the same huge proportions without the 'Stang, but it's hard to picture such an important era with Ford's pony missing from picture.

The car's background is pretty much an open, drama-filled history book. The Mustang had its highs and lows, starting with the great 1960s and early `70s and passing through the dark years of the second-generation model. Then there's the four-cylinder era, the "new edge" generation and the rebirth that came with the current model. With the 2015 Mustang just around the corner, a new chapter is about to begin as scholars dip their pens into inkwells.

And while we're all familiar with each generation and model of the of pony, there are numerous Mustangs that some of you might have never seen or heard of. Some of them were prototypes, others are just studies that have never seen the light of day, and some were real-life models. They've all contributed to the Mustang we know one way or another, but most of them are shadowed by the productions cars we've seen roaming the streets the past 50 years.

As you might have already guessed, we are here to introduce you to some of these concepts and studies, and to a couple of limited-edition models too, that came out of Detroit since Ford->ke31 began pondering about the Mustang.

More details after the jump.

1961 Avventura Concept

Right after Ford unveiled the Mustang I Concept in 1961, designers toyed around with numerous coupe bodies for the then new Falcon. The Avventura was the first fastback concept created around the said platform, and it featured a large hatch on the rear and a rear-facing, second-row seat. The Avventura never became more than just a sketch, but some of its cues would later appear on the fastback version of the first-generation Mustang.

1964 Two-Seat Concept

Ford imagined the Mustang as a two-seater as early as 1961. The initial goal was to develop an affordable version of the Thunderbird; a luxury two-seater introduced in 1955 and modified into a four-seater in 1958. Ford built a clay model of a shorter first-gen Mustang with only two seats in 1964, but the project never came to fruition.

1964 Four-Door Mustang

The company continued experimenting with various body styles in 1965, when it developed a four-door variant of the pony. But the idea wasn't good enough for Detroit's board of directors and it went straight to the trash bin. Thank goodness for that.

1966 Station Wagon Study

Naturally, the Blue Oval's daring designers also pictured a shooting brake-like, two-door station wagon->ke143 version of the first-generation Mustang. Although a running prototype was created in 1966, the Mustang wagon never made it to the assembly line. Although the station wagon is yet another body that would have ruined the Mustang as we know it, I have a feeling a grocery getter would've become a sought-after classic.

1966 Mach 1 Concept

The Mustang Mach 1 didn't arrive until the 1969 model year, but the first concept car was envisioned in 1966. Although its rectangular headlamps and low roofline were dropped in the approval process, the study actually became a production car, with most of its cues present on the gorgeous Mach 1 until 1971.

1967 Allegro II Concept

Based on an older concept, the Allegro II proposed a Mustang with Corvette->ke1280 Grand Sport-like speedster windshield and a competition rollbar. The rear end was totally different than anything previously seen on a Mustang, but the vehicle was far from being a pretty sight.

1967 Mach 2 Concept

The Mach 2 Concept was a revolution in terms of design, featuring a sportier body and the engine mounted behind the seats. Ford proposed the Mach 2 as a successor to the Shelby Cobra, but it spent its short career as an auto show queen.

1969 Mustang E

The first actual production Mustang from our list is a fuel economy minded model fitted with a 4.1-liter, inline-six engine mated to an automatic transmission with a special torque converter. Offered with a very low 2.33:1 rear axle ratio and without air conditioning, this rare Mustang was recognizable by the "E" lettering on its rear quarters. Only 50 units were built, which says a lot about the E's popularity.

1970 Mustang Milano

Showcased during the 1970 Chicago Auto Show, the Milano Concept previewed the long nose, the horizontal rear fascia and the overall sharp design that would eventually debut on the production 1971 model. Vaguely similar to the Dodge Charger, the concept eventually served as inspiration for Australia's Ford Falcon->ke442 XB.

1980 Mustang RSX

With all the rally->ke191 craze going around in Europe in the early 1980s, Ford commissioned Italian coachbuilder Ghia to create a rally machine based on the third-generation Mustang. Besides a brand-new body and an increased ride height, the RSX also gained a 5.6-inch shorter wheelbase and a one-inch wider track when compared to the production car. The vehicle was never built or homologated for racing->ke447.

1981 McLaren M81 Mustang

Penned right after Ford announced the formation of Special Vehicle Operations (SVO) in the fall of 1980, the McLaren->ke284 M81 Mustang was the result of a collaboration between Ford Design and McLaren Performance, the latter already famous for its motorsport endeavors and success. The heavily modified hatchback borrowed some cues from the IMSA race car, including the grille-less nose and the massive fender flares. Equipped with functional hood scoops, a heavy-duty suspension and BBS alloy wheels wrapped in beefy Firestone tires, the M81 'Stang received a gold-like orange exterior finish similar to that seen on most of McLaren's Can-Am cars and IndyCar->ke1559 single-seaters.

Power was provided by a turbocharged, 2.3-liter four-cylinder engine that generated 175 horsepower, 43 ponies more when compared to the standard 1980 Mustang. Production was initially set at 250 units, but only ten of them were eventually built, including the prototype. These limited edition Mustangs retailed for $25,000, which would mean nearly $70,000 as of 05/24/2014.