Tahu and the rest of the Toa Mata were created by the Great Beings in the planet of Spherus Magna. They were then kept in the Toa canisters and were in stasis.
The Toa canisters were supposed to be launched into the Matoran Universe following the events of the Great Cataclysm and land on the island of Mata Nui. The Toa's mission was to proceed through Kini-Nui, descend towards Metru Nui and continue on to awaken the Great Spirit. However, the malfunction caused the canisters to instead stuck in the space. For a thousand years, the canisters floated towards the atmosphere of the Matoran Universe until Takua collected the Toa Stones from Kini-Nui, which unwittingly activated a signal that summoned the canisters to the island.
Quests for the Masks
Tahu's Toa canister had arrived on the beach in Mata Nui. When Tahu emerged from his canister, he found that some of his mechanical components had separated. He then fused the pieces together and realized that he did not remember who he was or what he was doing there, much to his frustration. Tahu eventually remembered his name and discovered his fire powers. He then wandered into the forest where he was suddenly attacked by the group of Ta-Matoran, led by the captain of the Ta-Koro Guard, Jaller. They captured Tahu in a wooden Rahi trap but Tahu easily burned down the trap with his Fire Sword. The Ta-Matoran were about to attack him but Vakama, the Turaga of Ta-Koro appeared and stop the Ta-Matoran from attacking him. He then tell them that Tahu was a Toa and their protector. Vakama and the Ta-Matoran took Tahu to Ta-Koro, where he told gave Tahu a Kanohi Hau, the Mask of Shielding and told him about the Makuta called Teridax, who had tormented the Matoran for a thousand years. He informed Tahu that the only way to defeat Teridax was to gather the other five Toa Mata and collect the six Great Kanohi masks hidden throughout the island. After that, Tahu started on his journey to form the Toa Mata and find the masks.
Soon, Tahu met the other five: Gali, Lewa, Pohatu, Onua and Kopaka. They all shared tales of how they arrived in the Matoran Universe, with the exception of the reserved Kopaka. They then began discussing on how they will find the Kanohi masks. Tahu, Gali, Pohatu and Onua agreed that it would be best to search in pairs, while Kopaka and Lewa wanted to work alone.
Later, Jaller finds Tahu and told him the location of the Kanohi Akaku, the Mask of X-Ray Vision, was thought to be in one of the deepest caverns in Onu-Wahi. Tahu and Onua searched through Onu-Wahi and eventually come to a area with a deep pit in the middle and a long bridge stretching across to another ledge where tha mask is. Tahu started across the bridge when two pairs of Nui-Jaga, scorpion-like Rahi attacked him and Onua.