Announcer

The Announcer is a minor character in Portal 2, who has masculine programming and is voiced by Joe Micheals.

the Announcer appears to have taken over the Aperture Science facility as a back-up system, maintaining primary functions and stasis chambers. He continues this duty until the events of Portal 2, where he is most present in the beginning of the game, guiding Chell in test chambers through automated messages before After that, most major functions and decision making is  and the Announcer slinks back into minor managerial and production procedures.

He is an AI system designed to work in extreme and low power conditions to keep research and testing going, even during "circumstances of potentially apocalyptic significance” so “science can still be done.” Although, unlike many robots and AI in Aperture such as GLaDOS, Cores, or even Turrets, the Announcer does not have a physical presence and displays no hints of sentience. Instead, he rather is or is a part of the basic system of Aperture, his lines similar to computer alerts and triggered in the same fashion (such as deleting a file, indicating problems with the reactor core, etc.) He shows no acknowledgement to the outside the facility, no ability to record results from a test, no recognition of Chell being the one who, no desire to change tests within the facility or create new inventions, or ability to realize that the faulty turret used to sabotage the turret production line was flawed. He can, however, read files, detect life and the overall condition of the facility, operate the sprinkler system, as well as override the main AI in situations like stalemate procedures.

Indicated by his presence behind the scenes of Aperture especially concerning the production of Turrets, the Announcer maintains many ancillary functions that the main AI doesn't overlook but can utilize, and continues to make sure that miniscule problems are taken care of and that the main AI knows of any major problems occurring within Aperture.

Trivia

 * Several unused voice lines indicate that at some point during development of Portal 2, the Announcer's job was to be filled by GLaDOS herself, before ultimately being replaced by Joe Micheals' rendition of the script.