Several centuries before the Great Cataclysm, the Brotherhood of Makuta began kidnapping Matoran and experimenting on them, trying to create Toa without having to rely on destiny. An unknown number of Matoran were kidnapped initially, but only around sixty survived the experiments. Of those who survived, roughly half had became hideous, mutated creatures and were killed shortly thereafter. At this point, roughly twenty Matoran were left, each of them possessing enough power to rival a Toa, and while all of them were visually indistinquishable from normal Matoran, some were left with physical and mental damage. These twenty were subjected to Makuta brainwashing techniques and sent to various Makuta to be cared for and trained into Brotherhood pawns.
Unfortunately for the Brotherhood, the Matoran's minds recovered from their brainwashing after a few decades. One Nui-Matoran managed to kill his Makuta guardian and escape, causing the Brotherhood to order the deaths of all the Nui-Matoran. Some of the Nui-Matoran were able to escape before they were killed and have spent the years since then running and hiding from the Brotherhood and their minions.
Only nine surviving Nui-Matoran have been seen thus far.
- Raeser, an Onu-Matoran granted the power of telekinesis
- Pereti, a Matoran of Magnetism granted the powers of self-regeneration and quick healing
- Ihar, a Ta-Matoran granted the power of Rahi-shifting
- Nixan, a Po-Matoran granted the powers of super agility and reflexes
- Kyueni, a Ga-Matoran granted psychic abilities
- Taluu, a Matoran of Lightning granted the powers of illusion casting and sound recreation
- Oruni, an Onu-Matoran granted the powers of technopathy and super intelligence
- Tohra, a Po-Matoran granted the powers of super strength and invulnerability
- Rikka aka Ghost, a Ce-Matoran granted the powers of invisibility and intangibility
- The Nui-Matoran were originally created by Repicheep's real life brother when they were both much younger. Repicheep decided to resurrect the characters and give them a common origin story when he started Tales of the Nui-Matoran.
- Rikka, aka Ghost, was created by Inferna Firesword as a tribute to Repicheep's series. Repicheep has since included her in his "canon," though she is unlikely to appear beside the others as Inferna's stories that feature her take place much further into the future.