Opel is a German car manufacturer and the main brand in Europe for GM, who has owned the company since 1931.
German Opel automobiles were sold in US at Buick dealers starting in the late 1950's up until 1975. The 1975 models had fuel injection, which was considered such a big deal back then that it actually had a "fuel injection" emblem on the trunk lid. I used to have a 1975 Opel Manta, which was a good car mechanically, but the bodies seemed to be susceptible to rust and the interiors started falling apart after a few years.
GM tried to keep the Opel program going after 1975 by replacing the German built car with a Japanese one carrying the Opel nameplate. It was an Isuzu I-mark and they called it "Opel by Isuzu", but it was not very successful and Opel finally disappeared from the US market after 1979.