Text from: https://en.wikipedia.org/wiki/Cadillac_Fleetwood
The Fleetwood Body Company of Fleetwood, Pennsylvania, was founded by Harry Urich in the nineteenth century. It began as a small community of craftsmen founded by Henry Fleetwood, Esq. of Penwortham, near Lancaster, England (the Fleetwood family flourished in England in the 17th and 18th centuries). The rich traditions of 300 years of coach-building that the Fleetwood Body Company applied to its work on cars secured for it a high reputation in automobile circles worldwide by the 1920s. Coachwork was built by Fleetwood for a variety of luxury makes through 1924. However, after the Fisher Body Corporation purchased the Fleetwood Body Company in 1925, Fleetwood bodies were reserved exclusively for Cadillac. By 1929 GM had purchased the remaining stock holdings of the Fisher Body Corporation and thus became sole owner of both the Fisher and Fleetwood companies.
Originally an enclosed carriage, drawn by a single horse, for 2–4 persons, “Brougham” owes its name to British statesman, Henry Brougham. Cadillac first used the name in 1916 to designate an enclosed 5-7 passenger sedan body style. In the thirties, the name was given to a formal body style with open chauffeur compartment and enclosed rear quarters, metal roof and often “razor-edged” styling. When Cadillac started offering Fleetwood bodies on some of its cars in 1925, the Brougham body style was Fleetwood bodied every year with the exception of 1926. After 1937 the Brougham name was not applied to any Cadillac for the remainder of the pre-WW II period.
The Brougham name would eventually reappear on the 1955 Cadillac Eldorado Brougham show car which preceded the 4-door Eldorado Brougham hardtops of the 1957 to 1960 model years. In 1957 the Cadillac Series 70 Eldorado Brougham joined the Sixty Special and the Series 75 as the only Cadillac models with Fleetwood bodies although Fleetwood script or crests did not appear anywhere on the exterior of the car, and so this would also mark the first time in 20 years that a Fleetwood bodied car was paired with the Brougham name. Ironically, when production of the Eldorado Brougham was shifted in 1959 from the Cadillac Fleetwood plant in Detroit to Pininfarina in Turin, Italy, only then did it acquire Fleetwood wheel discs and doorsill moldings, presumably because the design work and final touches were still being done by Fleetwood. Production of the Eldorado Brougham ceased in 1961.
After a five year absence the Brougham name once again reappeared as an option package on the 1965 Cadillac Sixty Special. The following year the Brougham moved up to becoming a subseries of the Fleetwood Sixty Special. This continued through 1970. Starting in 1971 the Sixty Special was only available as the well equipped Fleetwood Sixty Special Brougham.
When the Sixty Special Series was retired in 1977, the Fleetwood Brougham took its place as Cadillac’s most luxurious owner-driven large sedan model through 1986.