Engineers, also called Inventors, were a type of job that Matoran held. Their job was to build machinery and other technical devices to improve the lives of other Matoran.
The job of engineer was most commonly held by Onu-Matoran, though other types of Matoran were also known to be engineers. One of the most famous examples of engineer, Nuparu, lived on Metru Nui prior to the Great Cataclysm. Among his earliest major inventions was the robotic Kralhi, created as law enforcement sentries; these proved ineffective, however, and were eventually replaced by Nuparu's next attempt at robotic law enforcement, the Vahki.
His second-most famous invention would be created centuries later, on the island of Mata Nui: During the Bohrok War, Nuparu invented the Boxor out of Bohrok parts, allowing Matoran to strike back against the Bohrok swarms.
Another engineer by the name of Velika lived on Voya Nui, and was responsible for creating the Zamor Launchers used by the Toa Inika, upgrading launchers stolen from the Piraka to carry four Zamor spheres instead of one to give them an advantage over the band of Skakdi.
A Le-Matoran engineer was known to have lived in the underwater village of Mahri Nui, who tried to harness the Hydruka's natural ability to shoot Solidified Air Bubbles and use it as a faster means of water travel than swimming. It was unsuccessful, but the engineer had no opportunity to fix his invention's flaws, as he happened to be in his own invention when it was launched into a nearby Tarakava and was promptly killed. Though it proved a failure, the invention was repurposed as a weapon for the Matoran to use against hostile water-breathers.