Thank you mate.The USAF/USN requires a new fighter aircraft to replace the F-15A/B/C/D model fighter and a new multi-role fighter to replace the F-16/F/A-18.
The USAF developed the F-22A through the ATF program which can be read about plenty of places online. The need was expected to counter the increasingly capable Soviet Union. Other "requirements" are being discussed now, but unfortunately the USAF has been a bit of a victim of it's own success in my opinion, by dominating so extensively over the past 30-40 years, they are now finding it somewhat difficult to buy the "shiny toys" the "fighter mafia" want for the new generation.
Hence the branding of the F-22 as an air dominance fighter vice air superiority fighter.
I've also read elsewhere the F-22 replaces the F-117 which is due to retire in 2008. This means the F-22 needs to fulfill the mission requirements of the F-117, which also implies the F-22 has deep strike characteristics the orginal F-15 may not have had.