Possibly the very first computer game I've ever played (since I was 4 years old I think) was Space Empires IV. SE5 is out, but I'm not really used to playing it. Space Empires IV came out in 1999 but is compatible with Windows XP up to Windows 7 (possibly newer OS as well). Have any of you heard of it?
I was able to create my own empires in that game very easily, as ai and race scripts can be edited in readmes. I took the Galactic Empire from the "Star Wars II" mod and created Zsinj's Empire, but I couldn't get the Zsinj icon working so I settled for Thrawn's portrait.