GLaDOS

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 a weird obsession with cakes.

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's Curiosity Core says the following when being defeated: "What's this? What's THAT? Where am I going?