Brief History from Wikipedia
The Sukhoi Su-27, NATO reporting name: Flanker, is a Soviet-origin twin-engine, super maneuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor to the large United States fourth-generation fighters such as the Grumman F-14 Tomcat and the F-15 Eagle, with 3,530-kilometre (1,910 nmi) range, heavy aircraft ordinance, sophisticated avionics and high maneuverability. The Su-27 was designed for air superiority missions, and subsequent variants can perform almost all aerial warfare operations. It was designed with the Mikoyan MiG-29 as its complement.
The Su-27 entered service with the Soviet Air Forces in 1985. The primary role was long range air defense against American SAC B-1B and B-52G/H bombers, protecting the Soviet coast from aircraft carriers and flying long range fighter escort for Soviet heavy bombers such as the Tu-95 "Bear", TU-22M "Backfire" and Tu-160 'blackjack".