The Mercedes-Benz W126 is the company's internal designation for its second generation S-Class, manufactured in sedan/saloon (1979–1991) and coupé (1981–1990) models, succeeding the company's W116 range. Mercedes introduced the 2-door C126 coupé model, marketed as the SEC, in September 1981. This generation was the first S-Class to have separate chassis codes for standard and long wheelbases (W126 and V126) and for coupé (C126).
The long 12-year production (1979–1991) resulted in 818,063 sedans/saloons and 74,060 coupés being built, totaling 892,123. W126 is so far the most successful and the longest in production for S-Class.
At the 1981 IAA Frankfurt, a coupé version of S-Class, C126, was introduced with 380 SEC and 500 SEC. It was the first time that a coupé version was derived from S-Class chassis. At the same time, the "Energiekonzept" (Energy Concept) was introduced to improve the fuel efficiency of S-Class through engine revisions.
Compared to its predecessor, the W116, the W126 featured improved aerodynamics with a drag coefficient of Cd 0.36 for the sedan/saloon and 0.34 for the coupés.