It was established in 1862 as a sewing machine builder, after which it expanded to producing bicycles, and finally, in the early 1920s, it became one of Germany's leading carmakers.
Opel's history as an independent carmaker didn't last long. By 1929, General Motors acquired the company's controlling stake. Two years later, the American corporation took complete control, turning the German brand into its European division.
After WWII ended, Opel's facilities were rebuilt with help from former employees and GM. Its civilian model lines were steadily reintroduced and improved, with the large Kapitän (Capitan) sedan being the company's flagship.
Becoming more American
Essentially, three distinct versions of the same model, the luxurious series included the Kapitän, which was now an entry-level offering, the mid-range Admiral, and the new range-topping Diplomat.
Since Opel's design and engineering departments were busy developing the B-series Kadett and the all-new Rekord C, the KADs were conceived with a lot of help from GM, which lent its RWD X-body platform and drivetrain components.
Therefore, the Kapitän, Admiral, and Diplomat were more or less European-bodied Chevy IIs (Novas).
Apart from the platform and drivetrains, the KAD series borrowed the popular luxury coupe recipe from the US in 1965, applying it to the newest and sexiest member of the model line: the Diplomat V8 Coupe.
Oozing muscle car vibes
Furthermore, it was equipped as standard with all the premium features available in a KAD model, making it the European counterpart to a US-built personal luxury car.
But, to European enthusiasts, it looked like a muscle car that had just crossed the Atlantic.
Almost twice as long as a Beetle, the imposing two-door Opel resembled a combination of the Chevy II Nova and Chevelle Sport Coupes.
Inside, however, the Diplomat V8 Coupe was more like a Buick Riviera, thanks to the plushy leather-upholstered bucket seats (front and rear) or the abundance of genuine woodgrain trims.
Chevy small-block power
Shared with the four-door Diplomat, the standard motor was a genuine 4.6-liter (283-ci) Chevrolet small-block V8 mated to a two-speed Powerglide automatic, both imported from across the pond.
At the time, the engine was listed with an output of 220 hp, according to the US gross ratings, but by the stricter German ratings, it made 187 hp.
In either case, the small block was by no means a muscle car engine, but it did help the Diplomat Coupe reach a top speed of almost 200 kph (124 mph). Better yet, it sang a beautiful tune that was unmistakably American.
However, legend has it that on the Opel test track and German autobahns (with no speed limits), the engine showed signs of premature wear after prolonged high-speed use due to inadequate cooling.
GM didn't want to tarnish the bombproof reliability image of its engine, so it instructed Opel to equip the Diplomat sedans and coupes with the performance-oriented 5.4-liter (327-ci) version of the small-block from 1966 onwards.
With this version, rated at 227 hp in Europe, the Diplomat could comfortably speed past the 200 kph (124 mph) mark, and, more importantly, the cooling issues disappeared.
A failed experiment
For starters, its sticker price stood in the same price range as a Mercedes-Benz flagship. Then, it was too big for European parking lots, gobbled up too much fuel, and its comfortable yet boat-like maneuverability seemed decades behind how a similar Merc handled.
Last but not least, there were the 4.6-liter's reliability issues, so when they put all those things together, potential buyers often opted for a proven, fully German Mercedes over what was essentially an American Opel.
Extremely rare and expensive today
Today, enthusiasts of this failed yet iconic model estimate that around 60 are still in excellent, road-worthy condition.
Because of its rarity and cult following, one of these surviving examples currently demands well over €100,000 ($107,613.50). To put it into perspective, a first-generation Diplomat four-door sedan in excellent shape usually goes for €30,000 ($32,275.65).
Even for that outrageous sum, most owners are reluctant to part ways with their V8 Coupes, so the chances of one popping up at an auction are slim to none.
Although it was a complete failure for Opel back in the 1960s, the Diplomat V8 Coupe is now one of the rarest, most sought-after European classic cars of its kind and one of the fewest that was developed using a genuine American recipe.
For a virtual tour of this captivating ride, we recommend the YouTube video below by Automobile Classics.