I was trying to think of something that sounds cool but not to pretentious, since it was 2006 and my username was Aegis which sounded cool but also way too pretentious. Since I was a shitnerd, I heard the word "Gyrfalcon" in American McGee's Alice and thought "hmm, if this was 'Gyrofalcon' it would sound like some robot bird." So, I changed my name to that. Quickly I realized that it was a shitty pun nobody would get, and started using the shortened version of just "Gyro."
I keep trying to think of a new username to go with. Candidates have included Sibboleth and FractalCat. Nothing really stands out though.