The 1956 Seville came out as a response to the Continental Mark II so Cadillac had a super-luxury coupe in the lineup. With the exclusive Eldorado body and interiors in full leather or special cloth/leather combos, the "Q" engine, and a Vicodec cloth-covered top, plus a $3,000 lower price than the Continental, AND the Cadillac name, it was quick and cost-effective move on Cadillac's part.
The Eldorado Brougham was supposed to debut as a '56 model, but it was delayed. The Mark II kind of stole some thunder from Cadillac that year, but, with the Eldorado coupe and the first Sedan deVille, it was a taste of things to come. What's more, the Seville outsold the Biarritz every year it was made. 1960 was the last Eldorado Seville and 1958 was the last year until 1967 that the Eldorado had a completely distinctive body style. The '59 and '60 came with standard air suspension. Eldorados also sported their own colors that were offered on the rest of the Cadillac models at extra cost. 1959 Persian Sand was one Eldorado color that became available on the 1960 cars, but it was replaced with Heather on the Eldorados for 1960.
1957 was the first year the "Seville", "Biarritz" and "Brougham" names appeared on the cars. The coupe and convertible sported their respective designations on the front fenders while "Eldorado Brougham" was only on the instrument panel. There were also four sedan Sevilles made in 1957 with Sedan deVille pattern interiors done in the Eldorado materials. There was a Bahama blue, Starlight silver copper and I think a black one. At least 2 or 3 of them have survived. The Eldorado Brougham sedan is a story of its own, but the "Brougham" name reappeared on the top-of-the-line sedans. "Seville" returned in mid-1975 as a new sedan. "Seville" also was used on a new DeSoto model in 1956.
Personally, I'd take one of each, or at least a time machine to take me back to those days...
Surely, Ford and GM would, too.