These have been really cool to read, so thank you all for posting! I hope more trickle in over time.
When did you join?
5pm PST June 15, 1999 when we redirected Sweet.Oblivion and the other game programming sites to the GameDev.net server. @Myopic Rhino, @Nick Murphy, and I had been running SO for about 2 years or so. SO was a merger of our individual sites. If I think all the way back to the very early formation of the universe, I think it was originally @Myopic Rhino's idea to collaborate.
What brought you here?
A passion for games and the technology behind game development, particularly in graphics and gameplay/simulation. My roots go back to learning from the 1990s demo scene and mode 13h. Who needs more than 320x240?
Why do I participate?
To give back. To learn and be inspired by the many who participate. To keep this community thriving.