Following the debut of the 1970s generation W116 (which also included the flagship Mercedes-Benz 450SEL 6.9), Mercedes-Benz began plans for the next-generation S-Class model. Codenamed "project W126," the project had specific goals: an improved ride, better handling, and improved fuel efficiency. These improvements were aimed at helping retain the S-Class' market leadership as the world's best-selling prestige luxury sedan. Following the 1970s oil crisis, Mercedes-Benz had made fuel efficiency an especially pertinent goal (named "Energy Program"), even in the large V8 engined versions of the S-Class.
In terms of the body design, the objective of the W126 design team, led by Mercedes-Benz's Bruno Sacco, was to produce a car that was sleeker and more aerodynamic (and thus lighter and faster) than the previous model. The application of lighter materials and alloys combined with thorough wind tunnel testing (to reduce overall drag) meant the car consumed about 10% less fuel than its predecessor; the maximum speed was also increased (250 km/h in the most powerful model).
After six years of development, the W126 was formally introduced at the Internationale Automobil-Ausstellung (International Motor Show, or IAA) in Frankfurt on September 1979. The initial lineup featured seven models in standard (SE, SD) and long (SEL, SDL) wheelbase sedan body styles: the 280 SE/SEL, 380 SE/SEL, 500 SE/SEL and 300 SD. Technically, the long wheelbase (SEL) variants were codenamed V126, but this was not popularly known. In 1981, the coupe version (SEC) of the W126 S-Class premiered at the IAA with the 500 SEC model. In 1981, Wheels Magazine selected the W126 model 380 SE as its Car of the Year.
Four years after the introduction of the fuel-efficiency "Energy Program," the model range had been reworked completely. In September 1985, again at the IAA in Frankfurt, the reworked model range was reintroduced. Apart from visual changes to the bumpers, side covers and alloys, the changes made to the available collection of engine variants was most visible. Two newly-constructed 6 cylinder engines and a new 4.2L V8 were added, and other engines were further upgraded.
The W126 generation was replaced by the W140 in 1992, although a satellite factory in South Africa is known to have continued production until 1994.
