Cobra is a codename for the writer of Portal 2012 blog. You can visit Cobra's blog here:
Cobra’s identity must remain veiled for now for various reasons. Cobra is a messenger for the Resistance Movement. Cobra himself/herself may or may not be part of the Resistance Movement.
What is important is the message and not the messenger. Human mind usually associates given message with perceived characteristics of the messenger and this tends to cloud its objectivity.