Buick Super Riviera Sedan
The Riviera name first entered the Buick line in 1949 as the designation for the new two-door pillarless hardtop, which was described in advertising as "stunningly smart." The Roadmaster Riviera (along with the Cadillac Coupe de Ville) constituted the first mass production use of this body style, which was to become extremely popular over the next 30 years.
In 1951 the "Riviera" designation was also used on a version of the Super 4-door sedan. The 1951 Buick Super Riviera 4-door sedan featured more plush interior trim and a wheelbase (and overall length) that was 4 inches (102 mm) longer than a regular Buick Super 4-door sedan. The Buick Super Riviera 4-door sedan was still an inch shorter in wheelbase and length than the larger Buick Roadmaster.
Starting in 1955 GM also offered a four-door pillarless hardtop body style, and the "Riviera" designation was also applied to these models. Riviera hardtop bodies were offered on all Buick lines in the next few years, including the Buick Roadmaster, Buick Super, Buick Century, and Buick Special. Since it was a body style designation and not a model, however, the Riviera name did not usually appear on the car. The last usage of the term "Riviera" to describe hardtops was 1963, as the formal designation of the #4829 Electra 225 Riviera four-door hardtop. Coincidentally, this was the same year the Riviera would become a separate model in its own right.
Source: Wikipedia, 2011