The Quadraplex T-3000 Computer (also simply known as the Computer or Computress) is Dexter's computer that oversees the running of the lab and has a personality of its own.
Computer is a big blue computer with a screen and a green line going across it that wobbles when she talks.
Computer is an advanced AI capable of some degree of genuine emotion and human-like behavior, however she is strictly loyal to Dexter and follows his every command. However she has shown that she might not think of Dexter too highly as seen in Game for a Game, where she acknowledged that Dexter was cruel and egotistical when compared to the spirited and friendly Dee Dee. In the same episode she also showed to posses very mature wisdom and a good conscience, strangely human-like traits for a mere AI. She will also not act unless ordered/suggested to by Dexter or someone else, as even when Dexter was misplaced in space, she made no effort to rescue him until Dee Dee inquired about his location, showing that her level of personal thinking might be limited. Nonetheless she still cares for Dexter as well as her own safety and appears to fear Dee Dee's destructive "playtime".
In Cartoon Network Universe: Fusion Fall, Computer (renamed Computress) is given far more human-like characteristics and actually shows to be capable of feeling love, especially towards the likes of Professor Utonium.