O'Malley/Omega
O'Malley is a homocidal Artificial Intelligence that was originally named Omega back at the research station. It moves between hosts via radio frequencies. A few years ago, it was implanted in to the armor of a young marine recruit named Tex. The aggressive intelligence of O'Malley would work with Tex's natural aggression, making her one of the most feared mercenaries in the known galaxy.
Shortly after Tex was hired to murder the red team in Blood Gulch, O'Malley caught wind of a cunning plan by Church to warn the reds of Tex's impending arrival, and left Tex's armor via long-range radio frequencies to enter Caboose's armor.
The small-minded Caboose stood absolutely no chance against the brutally cunning O'Malley. It quickly started turning Caboose's own mental images of those around him against him, driving itself deeper in to his psyche. It took Church and Tex entering Caboose's mind to forcefully drive the A.I. O'Malley from him.
As O'Malley left Caboose, it could find no radio signals to latch on to in order to continue surviving. It was about to shut down forever when it suddenly caught a radio transmission from Doc, and quickly entered its new host.
Again, O'Malley encountered little resistance within Doc. In a one-on-one battle between a homicidal maniac and a pacifist, the maniac is going to win every time, and this time was no exception. O'Malley quickly conquered Doc, and used him to attack both the blues and the reds, and to kidnap Lopez and take him hostage through the teleporter.
Once through the teleporter and safely on Sidewinder, O'Malley began plotting his Universe domination. He reprogrammed Lopez to do his evil bidding, and completed the weather control device Sarge had begun within Lopez. Then, something O'Malley wasn't expecting occured: the present was destroyed by a ten megaton bomb. O'Malley in Doc's body was sent to the future as if in a Delorean, where he claimed a new evil laboratory to continue his evil ways. Evilly.
Still set on taking over the Universe, he began building an army. His first recruit was the Red Zealot, but the recruiting process was cut short by the sudden (and rude) invasion by the Reds and Blues. O'Malley was driven out, but not defeated. He regrouped as Lopez built his brand new robot army, and began an assault on his former base. During the attack, however, he was attacked by The Great Destroyer. To this day, nobody knows what happened to him.
Just like Church, when O'Malley is in someone else's body he's simply that colour. His voice is much deeper than anyone else's, and he is often shot in extreme close-up mode.