|"I pleaded with them, I begged them to spare us! They asked what I had to offer. I offered ... my services. You must understand. I did this for you!"|
|— The mechanist explaining to Teo why he made Fire Nation weapons.|
The mechanist was an inventor and engineer from the Earth Kingdom who became a refugee after being displaced by a flood. He eventually resettled at the deserted Northern Air Temple during the Hundred Year War.
Living in poverty as a widower and left to care for his son, Teo, he was blackmailed into building ingenious weapons for the Fire Nation. Despite the hardships he faced, he still maintained an eccentric persona and his inventions contributed significantly to the development of technology in the world.
After a flood destroyed his village, killing his wife and leaving his son Teo a paraplegic, the mechanist led his people into the surrounding mountains in search of a new home. They came across the Air Nomads' long abandoned Northern Air Temple and promptly moved in.
Inspired by the airbenders, the mechanist mass-produced modified versions of their gliders, creating a whole new method of transportation for his people. He also devised an ingenious hot air-based power source for the whole temple, completely refurbishing and remodeling it in the process.
Among other inventions of his were time candles and a cut-safe knife sharpener which "only took [him] three tries to get it right", explaining the three wooden fingers on his left hand. A natural gas explosion similarly left him with patchy eyebrows.
Roughly a year after he and his people had settled, the Fire Nation blackmailed the mechanist into building new weapons, including steam-powered battle tanks, a war balloon, and plans for a massive drill, threatening to invade the temple if he did not comply. When Aang found out about this, he broke the arrangement the mechanist had with Qin, and the mechanist subsequently redeemed himself by aiding Aang and the others in repelling the Fire Nation when they stormed the temple.
The mechanist later returned to assist in the preparations for the invasion of the Fire Nation. Before coming ashore, he caused an explosion on one of the boats while working on his new invention, peanut sauce bombs, which Pipsqueak and The Duke seemed to enjoy as they commented that they were "destructive as well as delicious".
Due to the intellectual alliance of Sokka's plan and the mechanist's executions, the invasion force was able to use waterbending-powered submarines to sneak up unnoticed on the Fire Nation coastal guards. The mechanist did comment, however, that Sokka's original blueprints were "a bit difficult to decipher". The mechanist also presented Aang with a new glider with a built-in snack compartment.
During the invasion, he tagged along with the invasion force where he operated a supply truck filled to the rim with stone for the earthbending invaders. He narrowly escaped when a missile, shot from one of the battlements, blew up this truck.
He, along with the rest of the invasion force, later found out that his hot air balloons had been manufactured en masse and even upgraded to larger airships by the Fire Nation. The mechanist and the rest of the older members of the invasion force allowed themselves to be captured so that the younger ones could escape on Appa. He was sent to a prison after the invasion.
- Compressed-air elevator — Built for easy transportation between the many floors of the air temple.
- Earth Kingdom supply truck — Motorized, metallic vehicles, supposedly designed by Sokka in preparation for the invasion. They were used as a means of cargo transportation for earthbending ammo.
- Earthbending-powered tank — Vehicles owned and operated by the Earth Kingdom military. Used during the Day of Black Sun.
- Eclipse glasses — Wooden glasses with tiny slits for eyes, allowing one to stare into an eclipse.
- Finger-safe knife sharpener — Never seen. This invention took three tries to get right, resulting in the loss of three fingers.
- Fire bombs — Explosives released from gliders. Detonate on impact.
- Fire Nation drill — An enormous drill that the Fire Nation would later use to breach the walls of Ba Sing Se.
- Gliders — Several gliders, including Aang's new glider to replace his broken one and a chair glider for his son, Teo.
- Hot air balloon — Experimental weapon developed for the Fire Nation.
- Ice torpedo — Waterbending-powered weapon designed for use in the invasion of the Fire Nation.
- Peanut sauce bombs — Failed experimental explosive devices.
- Prosthetic wooden fingers — Three removable wooden fingers made to replace the ones the mechanist lost while making his finger-safe knife sharpener.
- Slime bombs — Thrown from hot air balloons and dropped from chair gliders. Exudes large amounts of a sticky, slippery, green substance that can immobilize entire tanks.
- Smoke bombs — Released from gliders. Obscures a portion of the battlefield and causes coughing.
- Stink bombs — Released from gliders. Emits a foul-smelling substance upon detonation that "no normal human can stand".
- Time candles — Candles used to tell the time.
- Timing device — Used to keep track of time during an eclipse.
- Tundra tank — Used by the Fire Nation as a strong assault force. They are equipped with a counterbalancing system that allows the tanks to remain face up after being flipped.
- Waterbending-powered submarines — Naval vehicles used in the invasion of the Fire Nation.
The mechanist was skilled at creating a variety of mechanical inventions, including weapons and a number of different modes of transportation. However, there was a limit to his capabilities, as was evidenced by his not being able to seal up the gas tank without any leaks. He also needed Sokka to help him complete the hot air balloon.
- The mechanist, Combustion Man, and the Ba Sing Se airship captain are the only characters to have a prosthesis.
- The mechanist's monocle was originally supposed to be a ring-shaped burn around his eye from a steam-powered telescope. However, the animators mixed up, and the script had to be changed.
- When observing the machines in the Earthen Fire Refinery, Sokka refers to the mechanist as "machinist".