As you're making your way through chapter 6 and 7, the fall and the itch, we get a lot of commentary from Aperture Science president Cave Johnson. At one point in one of these chapters Cave mentions Caroline, an employee he admired a great amount, that should be his successor if he happened to die. Cave does die, so it is implied that Caroline took over and was the last person to do so. And as we progress through the game we learn that part of Glados is Caroline's cognitive make-up. Even more interesting is why Cave would let Caroline be his successor, other than her just being an incredible assistant and employee. This is all speculation, but I believe Caroline is Cave Johnson's wife, mistress, whatever you want to call it, he loved her. These claims don't come without reason: Cave's endowment of his company to Caroline, the portrait of a lady and Cave and Glados reaction to this picture: "they look so familiar." I still have more ideas to further flesh out about this whole relationship and what it means, but right now i'm just trying to get it all worked out in my brain in a sound and logical way... for science, right? Or, in the vain of good narrative judgement.