1.) A cube in the game Portal you are given to help you with tasks.
2.) Your best friend.
1.)This weighted companion cube will accompany you through the test chamber. Please take care of it.
2.) While it has been a faithful companion, your companion cube cannot accompany you through the rest of the test. If it could talk - and the Enrichment Center takes this opportunity to remind you that it cannot - it would tell you to go on without it because it would rather die in a fire than become a burden to you.