The Aperture Science Weighted Companion Cube is a cube variant. It is physically a Weighted Storage Cube with a heart on it, but, to most players, it is much more than that emotionally. It has been theorized several times that Companion Cubes house dead bodies, but this theory is not accepted grudgingly tolerated on this wiki. It only appears twice in the Portal test chambers, once in each game. The level from the first game tasks you with destroying the cube, giving you the achievement "Fratricide." As a rule, it appears at least once in any fangame or map.

Companion Cube

A Companion Cube, as it appears in Portal.