Van Hohenheim

Trivia: The Portal 2 Companion Cube will hum a part of the "turret opera" when you're near. Probably AI in that box, if anything. We've seen the "Franken-cubes" too, so I find it more liekly Aperture would simply stuff AI cores into the cubes.

well, we can't really weigh cubes

I was comparing its weight by in-game behavior. It seems to be the same weight as a regular cube (though it is called Storage Cube, so there might be something inside those as well, though I tend to doubt it), compared to turrets and such which fall and roll a lot easier and with more bounce.