Tahu fell from the sky into the sea in a capsule with five other beings known to the people as Toa. Originally the capsules were intended to shoot into the space past the planet, but they instead fell into the sea. It would become their mission to free the island of Mata Nui, where they washed up, from the grasp of the evil Makuta and to save Mata Nui, the being for which the island was named, from his Makuta-induced sleep. The Turaga of Fire, Vakama, one of the leaders of the Matoran, mentored him in his missions.
Tahu was a member of the Toa Mata team, originally thought to be the first Toa team, whose members included Gali, Pohatu, Onua, Kopaka, and Lewa. They arrived on Mata Nui unaware of who they were. They found villages of beings called Matoran who had awaited their arrival to free them from the tyranny of the Makuta. The Matoran were led by wise beings called the Turaga who knew the Toa's names and purpose. It was their destiny to find all of the great Kanohi masks and use them to defeat Makuta who had polluted the minds of the animals of Mata Nui, known as Rahi, and put the Great Spirit Mata Nui to sleep. Tahu became the leader of the team, with Kopaka acting as the deputy.
In their first few journeys on the island, Tahu gained five other masks aside Tahu and his new Golden Mask from his Hau Mask of Shielding. The new masks gave him the powers of underwater breathing, x-ray vision, super speed, super strength, and levitation. At the temple of Kini Nui the six masks were combined into one golden mask that allowed him to use all of his mask powers at once.
The Toa then descended to the deep tunnels of the island where they faced shadow versions of themselves, created by the Makuta. They were victorious and reemerged and finished the task of reverting the Rahi to normal.
The Toa later faced the threat of the Bohrok swarms, mechanical creatures that functioned as suits for the Krata. The Toa gathered one of each kind of Krata and used them to unlock and activate the Exo-Toa, special power suits of armor. They then used these suits to battle the Bahrag twin queens. At the end of the battle they took off the armor to unite and use their combined power to imprison the Bahrag. The resulting energy burst threw them into pools of energized molten protodermis, transforming them into the Toa Nuva.
Once the transformation occured, Tahu became Tahu Nuva. His golden mask was turned into the Hau Nuva and was given a new look. It could no longer give him the powers of underwater breathing, x-ray vision, super speed, super strength or levitation, but he could extend his shield to those around him and the shield was no longer weak against ambushes. His sword was transformed into two more powerful ones that could be put together as a double sword or ridden as a surf board. Tahu nuva also had much greater fire control and could channel it through his swords in a variety of ways, including a heat or fire blast, slamming them into the ground, and sending out a stream of heat in the direction of the strike.
Shortly after the Bohrok Kal attempted to free the Bahrag, Tahu Nuva was given the Kanohi Vahi, the powerful Mask of Time, by the Turaga Vakama, who also cautioned him against its use. It gave him complete control of time. He used to defeat the Bohrak Kal by slowing time long enough for the other Toa to stop them from freeing the Bahrag.
Tahu can control and produce fire with almost no limit. Extensive use of his fire powers in a short amount of time can drain him but he can absorb energy from fire and heat to recharge. He wields a large fire sword that can cut through metal and stone. He posseses the Great Kanohi Hau that gives him the ability to produce a protective force field that can repel all attacks except for surprise ambushes. He is an adept lavasurfer and he surfs using a large rock for a board. His being is comprised of biomechanical metal called protodermis.