Cenert

Cenert is a Personality Core that was created for the sole purpose of rebuilding destroyed cores from turret wreckage. Cenert was in the background all the way to the events of portal 2, episode 1, and so he is first introduced there. Note this is in the Etheral universe, where Etheral created the place, had a son (his succesor), and built himself a device. Too bad for him, it went haywire, and he shut down. In portal 2, episode 1, Cenert succesfully rebuilds Etheral, who was drove mad with testing due to the shut down. Cenert appears as a core with a green eye and 2 arms that could fold into tools, and is a man character in portal 2, episode 1, where he rebuilds some systems (e.g. elevators), and destroys some (e.g. neurotoxin generators).

Quotes
"darn it, i just finished that device!"

"Do you smell that? Probably not, as i can not smell it. CORES DO NOT HAVE SMELL RECEPTORS!"

"I finally got that thing done and now you want to destroy it??!?? Well, i see why."

"Ok, done! Now rabbits can come out of this hat!"

Trivia

 * Cenert follows Wheatleys design, and as such is a moron.
 * You first meet him in the 3rd major test room, and then on he helps you destroy his "creation" as he calls it.