For a complete overview of all S-Class models see Mercedes-Benz S-Class

Mercedes-Benz S-Class

The Mercedes-Benz S-Class is a series of luxury sedans produced by Mercedes-Benz, a division of Daimler AG. The classification was officially introduced in 1972 with the W116 S-Class, which succeeded previous Mercedes-Benz models dating to the mid-1950s...

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The Mercedes-Benz W116 was a series of flagship vehicles produced from September 1972 through 1979. The W116 automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s were the first Mercedes-Benz

Mercedes-Benz

Mercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...

 models to be officially called S-Class

Mercedes-Benz S-Class

The Mercedes-Benz S-Class is a series of luxury sedans produced by Mercedes-Benz, a division of Daimler AG. The classification was officially introduced in 1972 with the W116 S-Class, which succeeded previous Mercedes-Benz models dating to the mid-1950s...

, although earlier sedan models had already unofficially been designated with the letter 'S' - for Sonderklasse or "special class."
The 'new' S-class generation development began in 1966, which was only a year after the launch of the W108/09.