The Omega Gate is the beginning of the path to the Core of planet Cybertron. Being the only means of entering the center of the Cybertronian homeworld, it was heavily shielded and all but impossible to break - it is likely that the combined military might of both Transformer factions would not even scratch it. It was believed that the Omega Key opened the doorway, but this is not the case. In truth, only Omega Supreme can open the Gate.
During the closing stages of the Great War, the Decepticon leader Megatron took possession of an orbital space station that manufactured the highly corruptive and unstable substance known as Dark Energon. Following the activation of the Geosynchronous Energon Bridge to create more of this energy source, Megatron intended to corrupt the entirety of Cybertron and thus win the war against the Autobots. To accomplish this, he first needed to gain access to the Core itself and thus laid siege to Iacon in order to acquire the Omega Key. However, the Key was not in its usual location as it had been taken by Zeta Prime thus forcing Megatron and his soldiers to journey into the Iacon Vaults to confront the Autobot leader. After defeating him, Megatron gained the Key, only for Zeta Prime to reveal that the relic merely alerted its Guardian, who had been activated in order to defeat Megatron. Despite the giant Autobot's valiant efforts, he was defeated and corrupted with Dark Energon, whereupon he was forced to open the Omega Gate and allow the Decepticons to corrupt the whole of Cybertron itself.
Upon learning of this, the Autobots fell under the leadership of the newly risen Prime; Optimus Prime and sought out to free Omega Supreme. After repairing him, Optimus along with his warriors journeyed through the Omega Gate in order to enter the Core of Cybertron so that they could purge it from the influence of Dark Energon.