Under GME s strategy, Opel and Vauxhall are twins. They sell the same cars in their own badges. Basically, all the cars are designed and engineered in Germany by Opel. The factory of Vauxhall just add production volume to Astra and Vectra. Opel also engineered Saturn L-series based on the Vectra. The same car provides the basis for Saab 9-3 and 9-5. 

Opel / Vauxhall is one of the big six car makers in Europe. Like Ford, Renault, PSA and Fiat but unlike Volkswagen, it produces the most common cars in all important segments - Corsa, Astra, Vectra, Omega, plus the MPVs Zafira and Sintra and a few niche models. It was never famous for innovation or build quality. 

Opel Astra

The first car designed by their own appeared in 1902, but until 1906 they built just 1000 cars of all kinds. The breakthrough occurred in 1909 with the Opel 4/8 hp model, which was modest but reliable and cheap. The success of this model, combined with advancer production system, meant that by 1914 Opel had become the largest German motor vehicle makers. 

Mass production came in 1924, helped it to regain the no. one spot of German sales chart in 1928. That year it sold 43,000 cars. The economic crisis in late 20 s result in the take over by General Motors in 1929. Like today, GM did not intervene the development of cars. With the support from GM, Opel out-performed the bankrupted Citroen and became the European no. 1 in 1935. By then the sales reached 100,000 cars annually. 

During the war Opel was quite lucky under Allies i bombing, thanks to the GM-link. After the war it was also the first to resume full operation. By 1950, production rose back to the 100,000 cars mark. However, through the years the company has little innovation or memorable cars created. Even the Opel GT of the mid-60 is was not really considered as classic cars by experts.  

Undoubtedly, the post-war sales chart was dominated by Volkswagen, except in the early 70 is when the production of Beetle declined. VW took back the lead with Golf and further rocketed away.