The origins of the Roadmaster name date to 1936 when Buick renamed its entire model lineup to celebrate the engineering improvements and design advancements over their 1935 models. Buick's Series 40 model range became the Special, the Buick Century took the place of the Series 60 and the Series 90 — Buick's largest and most luxurious vehicles — became the Limited. Buick's Series 80 became the Roadmaster, although it is commonly referred to as "sailboat", "tank", or "land yacht".
Roadmasters produced between 1936 and 1958 were built on Buick's longest wheelbase and shared its basic structure with senior Oldsmobiles. Between 1946 and 1957, the Roadmaster was Buick's premium and best appointed model, and was offered in sedan, coupe, convertible and station wagon bodystyles between 1936 and 1948.
In 1949 a hardtop coupe, designated "Riviera" joined the model line up; a four-door hardtop joined the model range in 1955. 1949 had the beginings of tail fins for Buick, and Buick's new automatic transmission, the Dynaflow.
Source: Wikipedia, 2011