Matoran Universe

The Matoran Universe was a system of "gigantic domes" inside the Great Spirit Robot. It was made by the Great Beings and watched over by the Great Spirit Mata Nui himself before Teridax succeeded in his Plan to control the universe.

History
The Matoran Universe was created by the Great Beings over 100,000 years ago as a giant mechanical being, who set Tren Krom to watch over it. When Mata Nui was created, he was set to watch over the universe, while Tren Krom was exiled to a barren island. Mata Nui's mission was to learn about the external universe and then return to reunite Spherus Magna.

When the Matoran Universe was about to launch, one of the Great Beings hid his mind inside a being from the Matoran Universe, to observe their creation.

The Brotherhood of Makuta and the Hand of Artakha were created, the former to create Rahi, and the latter to enforce order in the Universe. But the Hand didn't last very long, and was replaced by the Toa. The Order of Mata Nui was also created around that time, to carry out Mata Nui's will. The League of the Six Kingdoms once tried to overthrow Mata Nui and seize control of the Universe, but were defeated by the Brotherhood, the leader of which got an idea how Mata Nui could really be overthrown.

This Makuta, Teridax, soon took control of the Brotherhood and devised a plan to control the Universe. About 300 years before the Great Cataclysm, the Brotherhood infected Mata Nui with a Virus that gradually put him asleep. When Mata Nui finally fell asleep, a great earthquake shook the Universe, in an event known as the Great Cataclysm.

After the Great Cataclysm, one island in the Matoran Universe shot to the surface--Voya Nui. Mata Nui was also dying and was close to death when the Matoran returned to Metru Nui. The Toa Inika were sent to Voya Nui to recover the Kanohi Ignika, and heal Mata Nui. However, after they destroyed the cord connecting Voya Nui and Mahri Nui, sending Voya Nui back into the Matoran Universe, as Toa Mahri, they were too late, and Mata Nui died. The whole Universe would have been flooded in about three days, but Matoro sacrificed his life to revive Mata Nui.

However, life in the Universe was still in danger, because the the Brotherhood found a way into the Universe Core. A countdown was then triggered in the Ignika, at the end of which it would drain the life of all beings in the Universe. The mask soon realized it was a threat to the Universe, and eventually sacrificed itself and the body it created to fully awaken Mata Nui, by doing what would have taken the Codrex several days to do. When Mata Nui awoke, Makuta Teridax shoved Mata Nui's spirit out of his body and took control of it himself, successfully gaining control of the Matoran Universe. Mata Nui's spirit was banished to the Ignika, which was itself banished from the Matoran Universe. After Teridax finally gained control over the Universe he traveled to Bara Magna to fight and destroy Mata Nui. After battling him in an older prototype robot, Teridax was finally killed by a small piece of Aqua Magna, which had broken off during its flight through space. The Matoran Universe fell on the now recreated Spherus Magna. The inhabitants escaped and made new lives for themselves on their new home.