Starting with the 1965 Ford Mustang, the Ford Motor Company released a trim line identified by only two letters: GT. Thanks in part to the Mustang, those two letters have become associated with performance throughout the United States after having been predominantly a European suffix attached to the end of fine Italian sports cars, such as the 1960 Ferrari 250 GT (Gran Turismo). Since Ford Motor Company popularized the use of "GT", it has been used by many other models both in the US and around the world.
There were years where more limited production, high performance models
were offered, such as the Mach1, the Boss Mustangs, and the various
Mustang Cobras, there has been no performance trim line from Ford Motor
Company, or any other American make that has withstood the test of time
for such an extended period. Granted, the GT name was dropped briefly
in the early to mid 1970's, only to return in the late 1970's.
Nevertheless, the Mustang GT is probably the most well known and best
selling performance car and trim line ever built.