While the original purpose of the Plymouth was simply to cover a lower-end marketing niche, during the Great Depression of the 1930s the car would help significantly in ensuring the survival of the Chrysler Corporation in a decade when many other car companies failed. Beginning in 1930, Plymouths were sold by all three Chrysler divisions (Chrysler, DeSoto, and Dodge). Plymouth sales were a bright spot during this dismal automotive period, and by 1931 Plymouth rose to the number three spot among all cars.
For much of its life, Plymouth was one of the top selling American automobile brands, along with Chevrolet and Ford ("the low-priced three"). Plymouth even surpassed Ford for a time in the 1940s as the second most popular make of automobiles in the U.S.
Through 1956, Plymouth vehicles were known for their durability, affordability and engineering. In 1957, Chrysler's Forward Look styling theme produced cars with much more advanced styling than Chevrolet or Ford, although Plymouth's reputation would ultimately suffer as the cars were prone to rust and sloppy assembly. Because of its new "Forward Look" styling, however, 1957 total production soared to 726,009, about 200,000 more than 1956, and the largest output yet for Plymouth. The marque also introduced its limited production Fury line in 1956, and it too benefited from the crisp Forward Look designs.
Most Plymouth models offered from the late 1980s onward, such as the Acclaim, Laser, Neon, and Breeze, were badge-engineered versions of Chrysler, Dodge, or Mitsubishi models. Chrysler considered giving Plymouth a variant, to be called the Accolade, of the new-for-1993 full-size LH platform, but decided against it. By the late 1990s, only four vehicles were sold under the Plymouth name: the Voyager/Grand Voyager minivans, the Breeze mid-size sedan, the Neon compact car, and the Prowler sports car, which was to be the last model unique to Plymouth.
Source: Wikipedia Plymouth Article.