Originally Posted by Lucifer

Okay, for those of you not in the know, the weighted companion cube comes from the video game "Portal", in which your character is trapped in a research facility and guided by a friendly(?) computer voice has to solve a series of puzzle rooms with a special gun which shoots portals onto walls and floors. At one point you are given a 'weighted companion cube' to help you through the puzzle, but at the end of the level, you must destroy the cube in the incinerator. The computer voice reminds you for the rest of the game that you destroyed your only friend (the cube).
The companion cube has taken on a life of it's own in the mythology of the interweb, with plush toys, Halloween costumes, etc. If you don't believe me, search for 'weighted companion cube' on google or youtube.