D'ni Mosaic:
If you have completed the game, you will have been to D'ni, the place that you arrive in after you have used the green book in the library's fireplace. You will also notice that the floor is a mosaic, forming a picture of a man's face. That man is not Atrus, Sirrus, Achenar, or any other game character. The face belongs to Chuck Carter, who created a lot of the graphics for the game.