Mechanist and son Teo
This man is known as the Mechanist, and is a brilliant and offbeat inventor. He seems like a nice person, and certainly cares about his son, Teo. Although he can get so carried away with his inventions and scientific progress that he becomes oblivious to the destruction it has caused to his surroundings. (Like the historical artifacts of the Northern Air Temple). His eyebrows were burned off during a run-in with a gas leak in the temple's cellar while holding a torch, and although he jokes that he made a finger safe knife sharpener that only took three tries to perfect, I kinda doubt that's how he lost his three left fingers. I mean, the guy is a scientist, how could he make the same dumb mistake three times in a row? It doesn't seem likely.
Around a decade ago a flood wiped out his hometown, which took his wife's life and badly injured his infant son. He and the other refugees then left in search of a new home, until they came across the abandoned Northern Air Temple. Inspired by what the Air Nomads left behind and the desire to give his son a better life, the Mechanist began working on new inventions like a hang glider that anyone could use. He also installed a piping system throughout the temple that pumped hot air to power other inventions and keep the hang gliders afloat outside.
However, the refugees were only there for about a year before the Fire Nation discovered them. Threatening to burn the place to the ground, the Mechanist offered his services as an inventor in exchange for the temple & people's safety. They took him up on it, and from then on he began making weapons for them. Secretly turning the temple's sanctuary room into a workshop so the others wouldn't find out, he created new terrors like the Fire Nation tank and hot air balloon. But it wasn't until Aang visited the temple many years later did the secret finally get out, and he and Teo convinced the Mechanist to stop making weapons for the Fire Nation. But the damage was already done, and the Mechanist knew this. The Fire Nation had what they needed; they were now an even more threatening force.
This is Teo, the Mechanist's son. He was just an infant when the flood that took his mother's life happened, but during the event Teo was badly injured. His dad though created possibly one of the first wheelchairs in the world, just for him. Shaped kind of like a wheelbarrow, there's a lever for the brake and the chair connects to a glider. Assuming that it was first made when Teo was a small child or toddler, it was probably re-made many times over the years to match Teo's growing size.
Teo grew up at the Northern Air Temple, and probably spent a lot of his time mastering hang gliding. Inspired by paintings and gliders left behind by the Air Nomads, his father created hang gliders that non-airbenders could use, and a special glider that would connect to Teo's chair. It connects to the back of the chair and to the footrest, keeping the weight balanced and aerodynamic. There's also a small sack of special oil or something behind the chair, enabling him to write/draw in the sky. And he always wears his orange goggles when flying. ^-^
Teo is fearless, practically a hang gliding master, slightly resembles his father, and as Aang said, has the spirit of an Airbender. And while he's very proud of his father and his accomplishments, he's also upset with him because he was using his talent to build for murder. He also seemed rather troubled that his dad's justification for his helping of the Fire Nation was for Teo himself. Still, the two are in good relations, and hopefully won't have more trouble with the Fire Nation.