What is the name of the cube that GLaDOS encourages the player to bond with in Portal?

The cube GLaDOS encourages the player to bond with in Portal is the Weighted Companion Cube. It appears during Test Chamber 17, where Chell must carry it through a series of puzzles and use it to activate buttons and protect herself from hazards.

The cube is a special version of Aperture's standard Weighted Storage Cube. Its most recognizable feature is the pattern of pink hearts on its sides instead of the usual Aperture Science symbol. GLaDOS repeatedly describes it as a loyal companion and suggests that it may have feelings, deliberately encouraging Chell to treat an ordinary test object as a friend.

At the end of the chamber, GLaDOS orders Chell to place the cube in an incinerator. This moment became one of Portal's best-known jokes and helped establish the game's darkly comic view of scientific testing. The Companion Cube returns in Portal 2 with a slightly different design, and a charred cube appears near the end of the game. The shorter name “Companion Cube” is also widely accepted, but “Weighted Companion Cube” is the canonical full name.