Nachen is the guy who wrote IOS. Cisco keep him in an underground building called "the hive". They're currently performing scientific experiments on him in an attempt to decipher how he thinks the way he does.

No one knows his real name because after he wrote IOS, he changed it to Nachen in order to hide his identity from anyone who would want to cause him harm. It has been said that he is not from this world and requires complete darkness in order to work. This is why they keep him in the hive. There are multiple "work" rooms that are completely pitch black save for the light from the special monitor that he uses. These monitors were designed and built for his use, they are backlit with infrared lights. This means that the average human eye can't read it and thus, the whole room seems to be pitch black.

I once heard of a guy at Cisco that saw a passing document with his signature on it. This was the closest anyone has gotten to Nachen.

It is said that the only person that knows him on a personal level is called "Conf t". However, he (Conf t) is a whole 'nother story for a different time.

Keep it secret. Keep it safe.