Using certain soldier names in XCOM: Enemy Unknown will activate XCOM Heroes - pre-designed super soldiers such as Sid Meier and Ken Levine. Before activating a Hero, a pop-up will warn you that they're too damn amazing to allow you to continue the game with achievements turned on, and you cannot modify a Hero character after summoning it. If you decide to use one, do avoid killing him with some bull-headed tactical screw-up -- we'd kind of like BioShock Infinite to be finished.
The currently known XCOM Heroes are below - if there are more, someone will surely find them soon.
Here are some other XCOM tips you might be interested in:
Our fullsome XCOM strategy guide
Our video guide to playing Ironman mode
How to force the game to use 1080p cinematics.
The dev's own tips for taking down early-game ETs