Atlas is a blue eyed Core with a basic design as a typical rounded Core, and is portrayed to have somewhat more masculinity in its programming than in P-body. GLaDOS had created the Cooperative Testing Initiative after her awakening in Portal 2, as a means of replacing Chell as her only Test Subject. Along with P-body, the two bots are pitted against a series of tests built by GLaDOS herself, utilizing the many different mechanics previously encountered by Chell from the game's single-player campaign.
It was later revealed by GLaDOS that Atlas and P-body's Cores are programmed specifically to do nothing more but tests.
During the final phases of testing, GLaDOS reveals that, while the Cooperative Testing Initiative has its uses, she needs human testing for science, not robots. GLaDOS reveals that there are humans locked away, deep within the ancient Aperture facilities. There the bots will be tasked with navigating the old test chambers and unlock the massive vault containing the humans, seemingly kept in place by some form of cryogenic storage. By doing this, they 'save science.' However, almost immediately after the robots unlock the room containing the test subjects, they are destroyed. They are eventually rebuilt and, during the credits, Atlas sits at a computer desk and watches P-body playing on a conveyor belt.
