By the Earth year 2005, the Autobots had been completely forced off Cybertron by the Decepticons. Aside from small staging grounds on each of Cybertron's moons, their base of operations was Autobot City on Earth, a massive technological fortress where the Autobots lived and worked. In 2005, the Decepticons attacked the city without mercy, in an attempt to prevent an Autobot strike on Cybertron. Many Autobots died during this battle, including the great Optimus Prime.In the year 2006, the Autobot scientist Perceptor was heard to remark that during the great battle, the city's transformation cog was destroyed. At the time of the great battle, the city was only capable of transforming from city mode to heavily armoured battle station, but it seemed that the Autobot communications officer Blaster, and various other Autobots left behind on Earth while two small groups went to Cybertron and engaged the planet eater Unicron in battle, repaired and rebuilt a small section of the city into an independant, sentient fortress, which became known as Metroplex (Note: It is the opening shot of "Thief in the Night" which shows very clearly that Metroplex is only a small portion of the much larger Autobot City, which was eventually completely repaired). It was this sentient fortress that required the transformation cog to function. Blurr, Wheelie and Sky Lynx were sent to retireve a transformation cog from Marissa Fairbourne of Earth Defence Command, presently stationed on one of Jupiter's moons. Meanwhile, with help from the race of five-faced aliens known as the Quintessons, the Constructicons created a transforming Decepticon city of their own, known as Trypticon, which promptly attacked and destroyed the Ark. Blurr, Wheelie and Sky Lynx returned in the nick of time, and Pipes installed Metroplex's transforming cog. The massive Autobot transformed to robot mode, and fought Trypticon, hurling the saurian city into the ocean.

Metroplex's city mode is his natural form. He is completely aware of all that goes on inside him as long as he remains conscious. He can transform into a powerful battle station mode also. His robot form is immense, with great strength. In city mode, Metroplex has two security guards of sorts - Scamper and Slammer, two other small Autobots who have their own personalities, but are essentially extensions of Metroplex. Scamper transforms into a patrol car, but Slammer, on the other hand, is incapable of transforming, and his only mode is that of a tank. When he transforms to robot mode, Metroplex's rear tower become a large robot called Sixgun, who acts as an iterrogator. These three Autobots first appeared when Metroplex was next called into action.

When the Decepticon, Octane appropriated Trypticon from his resting place on Dinobot Island, he used him to steal national monuments as a way of paying Abdul Fakati, ruler of the arab nation of Carbombia, for oil which they could convert into super-energon. Metroplex was activated to stop Trypticon from stealing the Kremlin, but after a tussle, Metroplex was left holding the building, with no Trypticon in sight. The Autobots were blamed for all the crimes, but when they saved Fakati from the Decepticons, he explained to the public that the Autobots were not to blame.

Metroplex continued to act as Earthbase for the Autobots. He once had his eyes stolen by Scourge and Starscream's Ghost as part of a bargain with Unicron, but they were later restored. He also had his transforming cog stolen at one point, by the Combaticon, Swindle, and the Autobots retailiated by stealing Trypticon's cog. The stolen cogs were installed in the oppostite cities, rendering their transformations unstable, but the Protectobot, First Aid aligned Trypticon's cog correctly inside Metroplex, he was able to beat Trypticon yet again.

Metroplex's last recorded appearance was when the Hate Plague was sweeping Earth. In order to protect him against contamination, then-Autobot-leader Rodimus Prime deactivated Mertroplex. Metroplex was aware of the situation, and understood that Rodimus had to do it. Metroplex was never seen again afterwards, and it remains unknown if deactivating him sent his spark off-line, or if he was later reactivated at some point after the restoration of Cybertron's Golden Age.