The F-15, the USAF's tactical air superiority fighter of the 1980's. But for the 21st century, it was becoming old. Built to replace the F4 Phantom, it was a fast, maneuverable, long range fighter. But it was not stealthy.
In the 1990s Boeing and the so called, skunk works, aka, Lockheed Martin, had a new prototype ready to fly. The YF-22 Raptor
The YF-22 was the prototype of the now know F-22 Raptor. The first flight of the F-22 was on Sept. 7, 1997.
http://www.lockheedmartin.com/us/100years/stories/f-22.html
//www.boeing.com/boeing/history/boeing/f22.page