The fastback joined the original Mustang lineup after the hardtop and convertible. Ford introduced the fastback 2+2 in August 1964, adding a dramatically sloping roof and enclosed rear cargo area to the Mustang range.
The hardtop offered a formal coupe profile, while the convertible provided open-air motoring. The fastback gave the Mustang a more sporting appearance and greater visual connection to European-style grand touring coupes. Its rear seats remained small, but the design made the car especially appealing to enthusiasts.
The fastback’s roofline also changed the practical character of the car. Rather than a separate trunk opening, the sloping rear section enclosed the luggage space under a large rear hatch area. This made the fastback useful for carrying more bulky items than the other early body styles.
Later Mustang performance icons, including the Shelby GT350, were closely associated with the fastback shape. “Fastback” is the canonical answer here; “SportsRoof” became Ford’s later marketing term for related versions.