Onepu was an archivist on Metru Nui. However, he was too adventurous to wait for Rahi to be brought in by Vahki. His most famous expedition credited him with finding the first Bohrok. He also helped Mavrah with an experiment on ancient sea Rahi, but the experiment was later abandoned. He was eventually captured by the Vahki and placed in a Matoran Pod. Eventually, Onepu was brought to Mata Nui by the Toa Metru.
On Mata Nui, Onepu lived and worked in Onu-Koro as the captain of the Ussalry. He was also a very skilled Ussal Crab rider and once won the great race. He was also Whenua's right hand, and was called for advice many times. He was eventually rebuilt into a taller, stronger form at Kini-Nui. He was one of the Matoran that helped construct boats for the return trip to Metru Nui.
Return to Metru Nui
Following the Matoran's return to Metru Nui Onepu helped to rebuild the city until the Staff of Artakha did the rest of the work. He was also present during the ceremony for Matoro.
In 2001, Onepu was released as a promotional set by McDonald's. His set number was 1389.
His set contained 8 pieces.
Onepu, along with the other promotional Matoran, has the fewest pieces of any Bionicle set released to date.
Onepu is one of the two 2001 McDonalds Matoran sets to not become a Toa Inika (the other being Macku).
Onepu was the only McDonalds Matoran to not have another set release after his release in his weakened Matoran form as Macku would be released in her rebuilt form, and the other 4 would become Toa Inika. Though 3 of these Matoran were also released in their rebuilt forms.
Onepu was the first Matoran to see Onua upon his arrival on Mata Nui.