The Mask of Light

The Kanohi Avohkii was the only Mask of Light in the main timeline

History
Thousands of years ago, the Avohkii was created at the island of Artakha. It was meant to be insurance against the possibility that the Brotherhood of Makuta might betray their duty. 2,500 years ago, the Brotherhood did turn evil and Makuta Kojol led a strike force of Rahkshi, Exo-Toa and Visorak into Artakha, overcame its defenses, and retrieved the mask so the Brotherhood could guard it. 1,300 years ago, the Toa Hagah discovered that the Brotherhood had stolen the Avohkii. They turned against Teridax and temporarily defeated him. Although Roodaka mutated them into Rahaga, they were able to steal the Avohkii from a Brotherhood of Makuta fortress. Seeking a reversal for their mutation, the Rahaga sought out the legendary Rahi Keetongu while trying to protect other lands from the Visorak hordes, carrying the mask with them throughout their quest.

1,050 years ago, the Rahaga eventually settled in Metru Nui, hiding from the Matoran by hiding in the Archives. The Avohkii was kept safe in a special chamber only unlockable by the Makoki Stones.

Fifty years later, after the Great Cataclysm occurred, the Visorak finally invaded Metru Nui. The Rahaga sent the Toa Hordika on a mission to retrieve the Avohkii from its chamber before the Visorak could get to it. To do so, the Toa Hordika first retrieved the six Makoki stone fragments hidden by the Rahaga. After they found it, Onewa used his Rhotuka to encase the mask in stone to conceal the Avohkii's glow from the Visorak. After the Toa Hordika were changed back to Toa Metru and transported the Matoran to the safety of Mata Nui, Vakama later had a vision concerning the Avohkii's use in the future. In his vision, he discovered that the mask was to be kept hidden from the Matoran. One day, an adventurous Matoran would find the mask, and they would take on the role of Herald of the Seventh Toa, charged with bringing the mask to its rightful owner, the Toa of Light. Therefore, the Turaga carved the stone shelled over the mask into a warning totem, placed it on the far end of a lava tunnel, and waited for the day when destiny signaled the mask was to be used.

A couple months ago, Takua the Chronicler found the mask right before Mata Nui's championship Kolhii match. After he and his partner Jaller lost to Ga-Koro, the Avohkii slipped out of Jaller's pack and into view before the Turaga. Takua, not wanting to take responsibility for the mask's appearance, positioned it so that its glow fell on Jaller. The Turaga took the mask at once to the Ta-Suva, where Nokama deciphered the writings on the inside of the mask. It became official--Jaller was clearly meant to be the Herald of the Seventh Toa. Takua was chosen to accompany him to chronicle the journey.

Jaller, Takua, and Pewku followed the direction in which the mask shone brightest from Ta-Koro through Le-Wahi, Ko-Wahi, and Onu-Wahi. It was in these dark caves where Teridax threatened Takua to give up the mask so he would spare Jaller's life. Takua, afraid to take definite action, left Jaller to continue the quest alone. After three Rahkshi attacked Onu-Koro, however, Takua regretted his decision and rushed back to join him again. Reunited, Takua and Jaller eventually came to Kini-Nui. Incredulous that such an obviously sacred site could be the Toa of Light's location, Takua took the Avohkii from Jaller's hands himself. When Takua shook the mask, a laser beam shot from the mask and broke apart a portion of the giant stone bust of a maskless Matoran head that overshadowed the Amaja-Nui. Six Rahkshi, aiming to kill the Herald and take the mask then approached. Takua then proclaimed to Jaller that he was the true Herald, as he had clearly been all along, and the two ran to the Amaja-Nui to hold off the Rahkshi.

Working together against the Rahkshi, the Toa Nuva quickly defeated them. All but one Rahkshi did not rise again. As Turahk spread its fear into Takua and prepared to kill him, Jaller leapt at the Rahkshi. He clung to Turahk's staff, but the fear energies overtook his body, and died as Takua knelt over him. Saddened and given hope by his best friend, Takua donned the Avohkii. It was then that he found the Toa of Light--in himself. The energies of the Avohkii suddenly coursed through Takua, transforming him into Takanuva, the Toa of Light.

Eventually Takanuva faced off with Makuta Teridax himself in Mangaia. As events unfolded, the Toa, Turaga, and Matoran were able to rediscover Metru Nui and return to it. While guarding the coast of Metru Nui, Takanuva was attacked by a Shadow Leech, causing his mask to change shape and become gunmetal in color. Its powers remained the same, and it eventually reverted to its original size, shape, and color after a Klakk restored Takanuva's light. In The Kingdom, an alternate timeline, Takanuva fullfilled his destiny with the aid of the Order of Mata Nui by driving the Brotherhood of Makuta away from the city of the Great Spirit. Afterwards, he became a Turaga, causing the Kanohi Avohkii to turn into a Noble Mask. It is unknown what the Noble Avohkii looked like.

Powers

 * Great: The Great Kanohi Avohkii gave its user a Toa-level range and strength of Elemental Light powers. It also gave them the power to bring understanding to the hearts of others. Despite the fact that it was one of the few elemental Kanohi, it did not boost any pre-existing Elemental Light powers the user might have. Additionally, the Avohkii allowed its user to sense moral light in others.
 * Noble: The only difference between this and the Great Avohkii was that the Noble Avohkii allowed its user Turaga-level range and strength of Light powers and the duration of its effects were shorter.