Tahtorak

Tahtorak were massive 40 foot dragon Rahi that could speak Matoran. Their homeland was an island south of Metru Nui that was also home to Keetongu's species.

The species were also found on Zakaz, where the Skakdi had been known to use them as mounts. The Tahtorak there planed to overthrow the Skakdi, but were waiting for the right moment.

The Tahtorak of Metru Nui
Only one Tahtorak has been seen so far, in Metru Nui, and it constantly demands "Give me the answer!" without asking his question which is believed to be "How did I get here?" That Tahtorak was last seen disappearing into the Zone of Darkness with Krahka and Zivon. It has since been revealed that it was Brutaka who dropped it into the center of Metru Nui just for fun.

1,000 years later, a wormhole, created by Brutaka, appeared and Krahka and Tahtorak apppeared on Voya Nui. Krahka was able to fly away, but Tahtorak was stranded. It is known that after the Tahtorak defeated the Kardas Dragon, Axonn summoned Botar back to Voya Nui. Showing a rare sense of humor and justice, Botar teleported the Tahtorak to the island of Xia, where it went on a rampage, during which it was stopped from killing Roodaka by the Toa Nuva. After the Toa Nuva left for Karda Nui and Roodaka left for the Federation the Tahtorak was defeated when Bomonga used his mask of growth to punch it to the ground and Pouks used stone bonds to keep it there.

Trivia

 * Tahtorak was a winning design in the Rahi Beasts contest
 * Tahtorak was on the cover of the Rahi guide
 * "The Tahtorak of Metru Nui" isn't an offical name, just a nickname