Illuminati

Illuminati usually refers to a purported clandestine organization which runs the entire world, carefully calculating and planning everything that happens in secret. The Illuminati are briefly mentioned in the Zombies levels Shi No Numa, Der Riese and Kino der Toten by Edward Richtofen. It should also be noted that Richtofen himself is a member and possibly the Pentagon Thief as he has Illuminati code imprinted on his clothes.

Codes
There are multiple codes and references of the Illuminati in the Zombies game mode.

Der Riese

 * There is a note with Illuminati code hidden in a drain in the spawn room.
 * More coding is written on a wall behind the barricade to the left of the Pack-a-Punch machine.
 * There is a code written on the white door in the room next to the Type-100.

Kino der Toten

 * The Eye of Providence is found inside a book on a bookshelf behind a barricade. This barricade is located next to a meteor fragment in the room leading to the stage.
 * Richtofen, upon getting the Ray Gun from the Mystery Box, may say "The Illuminati will never get their hands on me again."

"Five"

 * The Eye of Providence can be seen briefly on any television showing the location of the Mystery Box. The TVs are turned on when the power is.

Trivia

 * At the start of the Black Ops mission "S.O.G.", the word 'Illuminati' can be seen on one of the classified documents.
 * The Illuminati are referenced repeatedly in Zombies, mostly through quotes.
 * On Der Riese, multiple notes can be found written in Illuminati Code can be seen.
 * On one of the screens in "Five" and "Ascension" Zombies map, an all seeing eye pyramid can be found. The all seeing eye is often associated with the Illuminati.