Arguably the most successful Italian aircraft of the post-war era, the Fiat G.91 was designed by Giuseppe Gabrielli for the highly lucrative 1953 multi-national NATO requirement for a lightweight strike fighter for its European air forces. The G.91 was a small and nimble fighter with prominent swept wings and a nose-mounted intake similar to the F-86 Sabre but despite winning the competition was only adopted by a very small number of other countries due to the French abandoning the process to develop its own Etendard and the British concentrating on the Hawker Hunter. Nevertheless, the superb G.91 went on to have a distinguished 30 year career with the air forces of Italy, Germany (where it was built locally by a consortium led by Dornier) and Portugal, the last of which were retired as late as the mid-1990s. It was also evaluated or considered by a number of other nations including the United States.

The prototype G.91 first flew on 9 August 1956 and entered service three years later with the Aeronautica Militare Italiana as the G.91R/1. Further improvements by Fiat led to the G.91R/1A with upgraded avionics and the G.91R/1B with newer Fiat-built engines. Luftwaffe versions included the G.91R/3 with 30-mm cannon and the G.91R/4 which reverted to the earlier machine guns. With Portugal receiving second-hand German units, the only other variants ever developed were a tandem two-seat trainer known as the G.91T as well as the G.91Y for the AMI. This was the ultimate version of the G.91, increasing performance considerably thanks to a twin-engine configuration and additional avionics. It was phased out only until 1995.