Hiroshi Sato is the maker of the Satomobile, and not only that. He makes weapons for the Equalists and he's apart of the Equalists. The reason being is because he's holding a grudge against benders for killing his wife. A firebender killed Mrs.Sato. When Asami Sato, Hiroshi Sato's only daughter (and child), finds out about this action she turns against him. Therefore, Hiroshi went against his people just like councilman Tarrlok did.