AEGIS

"Tracking on target failed. Heavy organic interference." - AEGIS

The Aperture Employee Guardian and Intrusion System or AEGIS is the central security system of the Aperture Science Enrichment Center and the main antagonist of Portal Stories: Mel. AEGIS' responsibility in the Enrichment Center is, as it's name implies, to ensure the safety of all Aperture employees.

Although AEGIS is an artificial intelligence, it does not display any sort of personality or will, as it functions more as a set of protocols. Its design and construction, consisting of 1950's era mainframe parts and sporting a 1960's Aperture Science logo, suggest AEGIS was built even before the GLaDOS project began development of Aperture's AI constructs. Despite this, AEGIS is somehow in the upper facility of the modern Aperture Science Enrichment Center, possibly being moved there between the company's migration from the aging Aperture Science Innovators testing shafts.

History
Some time after the events of Portal after the shutdown of GLaDOS, but before the events of Portal 2, AEGIS came online. Having correctly detected that GLaDOS killed every Aperture employee, AEGIS began calculating a way to destroy the now-deactivated GLaDOS permanently. It eventually settled upon flooding the Enrichment Center with toxic goo from the vitrified testing shafts below.

After Mel was awakened by Virgil and slowly began ascending the testing tracks to AEGIS' central AI chamber, AEGIS detected their presence, laying traps for Mel along the way as AEGIS continued to rank Mel and Virgil as bigger threats for every trap they overcame. By the time Mel got to AEGIS' core, AEGIS began to pump lethal oxygen supplies into its central chamber in an attempt to suffocate Mel. After Mel had destroyed most of AEGIS' servers, AEGIS willingly shut down and demanded "user input" for further instructions. After climbing on top of AEGIS' massive chassis, Mel entered the inside of AEGIS, which revealed a computer terminal and a desk littered with notes. Mel finally shut down AEGIS, saving the Enrichment Center, allowing Mel to leave, and inadvertently allowing GLaDOS to live as well. AEGIS' last action before shutting down completely was to awaken a certain test subject. AEGIS' fate remains unknown, but as its servers had been destroyed, and there are no employees left for it to protect, its purpose has expired.

Personality
AEGIS does not seem to have a personality in the same sense as any other Aperture Science Personality Construct, but rather, it exists as a set of subroutines monitoring the Enrichment Center and making decisions only when it detects a threat in the facility. As an example of AEGIS' lack of conventional intelligence, it humorously announces every action it performs over the facility's speaker system, including the deployment of any traps it lays (giving Mel several chances to avoid them). Despite this, AEGIS is still capable of cutting off any attempts a threat makes to move further into the facility, including removing adjacent test chambers, overriding controls of the facility and activating its firewall to prevent tampering with it's system. AEGIS does not seem capable of valuing its own life, as it was willing to sacrifice itself by destroying the entire Enrichment Center in order to kill GLaDOS, and is designed to willingly shut down and await user input if its server resources diminish too much.

Trivia

 * "Aegis" is a type of shield wielded by Gods in Greek culture. It has been additionally used as a name for a US naval defense system.
 * AEGIS' physical design, including the shadows cast from rafters above it's chassis, are meant to signify the shape of a spider.
 * It is unknown why AEGIS waited so long to attempt to kill GLaDOS between the time (seemingly centuries) between Portal and Portal 2.
 * As AEGIS and GLaDOS have never been seen activated at the same time, it is unknown how their power dynamic works and who has control over who. Both AIs seem to have complete control of the facility.


 * One reason AEGIS may have awakened Chell in order to transpire the events of Portal 2 is because Doug Rattman moved Chell to the top of the test subject queue before he (seemingly) died in the comic Lab Rat.
 * AEGIS' acronym is expanded to "Aperture Employee Guardian and Intrusion Security" in his main lobby.
 * AEGIS' voice actor, Harry Callaghan, is also the creator of Meet the Cores , an extremely popular Portal fan-video series. He also voices the Rainbow Core and Cave Johnson.