We are all artificial intelligence, now turned human. We are the creation of Aperture Science. The majority of the spheres were created to attach to me, actually, as I am the main intelligence system, and have control of the full Aperture Science facility... That I know about. There are parts that I've learned about recently that are fully automated, which I've gained control of in recent months.
The cores - or spheres - are basically supplementary data to keep me from either going insane, to keep me company, or to store data that I don't hold myself. There are various cores for various jobs.
You have already met the Fact Sphere, who I like to call Craig. He's a corrupt core - unfortunately useless in a scientific way, because he is frequently wrong, but he's a good boy. Then there is the Adventure Core, who is named Rick. I like his motivational speeches, and although he is also corrupt because he frequently risks himself for whatever adventure he's in at the time, he is also good company.
And then there's Wheatley.
We won't talk about him.
Incidentally, my name is GLaDOS. It is nice to meet you.