"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 Nationweapons.
Living in poverty as a widower and left to care for his son Teo, he was blackmailed into conspiring with the Fire Nation to build ingenious inventions of artillery for them. Despite his wretched life, he had quite an eccentric persona. 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 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 the airbenders' gliders, creating a whole new method of transportation for his people. He devised an ingenious hot air-based power source for the whole temple, completely refurbishing and remodeling it.
Among other ingenious inventions of his, were time candles and a cut-safe knife sharpener. This "only took [him] three tries to get it right", explaining the three wooden fingers on his left hand. A natural gas explosion left him with patchy eyebrows.
Roughly a year after they settled, the Fire Nation blackmailed the mechanist to build new weapons, including steam-powered battle tanks and a war balloon, under the threat of invading 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 redeemed himself by aiding Aang and the others to repel the Fire Nation when they stormed the temple.
He drew up plans for the massive drill, eventually completed by Qin and used to penetrate the Great Wall of Ba Sing Se. This proves that the Fire Nation soldiers were apparently able to steal the drill plans sometime during the attack, along with recovering the downed hot air balloon after their defeat.
The mechanist returned to assist in the invasion plan. Before coming ashore, he caused an explosion on one of the boats where he was 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 submarines had many functions such as transportation, and were equipped with torpedo tubes from which the waterbending passengers could fire the ice torpedoes. 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 earthbender 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 mass 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.
After the Hundred Year War ended, the mechanist was freed and reunited with his son, Teo. The two attended Zuko's coronation as the new Fire Lord at the Fire Nation Capital.
Compressed-air elevator — Built for easy transportation between the many flights of the air temple.
Earth Kingdom supply truck — Motorized, metallic vehicles. They were supposedly designed by Sokka in preparation for the invasion. They were used as a means of cargo transportation for earthbending ammo.
The mechanist seemed to be very intelligent at creating machines, weapons, and all sorts of mechanical inventions. However, there was a limit to his capabilities, such as not being able to seal up the gas tank without any leaks. He also needed Sokka to help him complete the hot air balloon. However, he came up with many good inventions such as gliders, tundra tanks, and finger-safe knife sharpeners.