GLaDOS
Role
The deceitful computer, GLaDOS (which stands for Genetic Lifeform and Disk Operating System), is the speaker and controller behind the Aperture Science Enrichment Center. She has an odd obsession with cakes.
Origin
GLaDOS was created in response to the news that Black Mesa was developing a portal technology similar to that of Aperture Science. Her original purpose was to be an artificially intelligent research assistant (and disk operating system). Work on GLaDOS started in 1986, and was under development for more than ten years before she was finally completed several years after 1996. GLaDOS was activated for the first time, untested, during one of the events on Aperture Science's first annual "bring-your-daughter-to-work" day.
In many ways, the initial test went well...
GLaDOS is made up of several "personality cores" in the form of strange spheres that apparently control the AI's behavior. Chell encounters a morality core, curiosity core, cake core, and anger core (in that order) while destroying GLaDOS.
GLaDOS's Curiosity Core says the following when being defeated: "What's this? What's THAT? Where am I going?