Fire Nation Man was an earthbender who fought in the Earth Rumble VI tournament in the town of Gaoling. However, "Fire Nation Man" was only a stage name, and he was not an actual citizen of the Fire Nation. His role was that of a heel: to be hated by the audience, then defeated instantly in order to generate enthusiasm for other fighters.
Fire Nation Man carried a Fire Nation flag, wore a red cloak, and sported a stereotypical Fire Nation hairstyle; he somewhat resembled AdmiralZhao, though not in physique. Even though his stage name was "Fire Nation Man", he was really an earthbending fighter. He acted like a Fire Nation citizen and was easily defeated just for show. In Earth Rumble VI, he was quickly defeated by The Boulder in the tournament. When all of the Earth Rumble fighters kidnapped Toph, Fire Nation Man was defeated almost effortlessly by her.
The Fire Nation Man seemed to prefer using dirt-based attacks, as opposed to solid rock. When attempting to subdue Toph, he arrived in the ring using a dust tornado and earthbent a large stream of dirt at Toph. This would be consistent with a desert upbringing, where sandbenders specialize in bending loose earth. The technique also vaguely resembled firebending, which played into his persona.
Fire Nation Man showed a resemblance in his entrance to that of many "bad guy" foreign wrestlers, most notably Nikolai Volkoff who was known for singing Soviet Union's national anthem prior to his matches in the WWF, much to the crowd's dismay. Another point that linked the two was his aforementioned thick accent, which sounds stereotypically Russian.
Additionally, the boots that Fire Nation Man wore had the pointed tip at the end, in the style of The Iron Sheik.
According to DVD commentary, Fire Nation Man was an immigrant from the Si Wong Desert.
Even though it is not confirmed how the Fire Nation Man thought about the Fire Nation himself, he was the only earthbender or Earth Kingdom citizen during the series who officially claimed to be a proud supporter of the Fire Nation. Other Earth Kingdom citizens who supported the Fire Nation during the series did so due to self-interest or were forced to against their will. However, since the publication of The Promise trilogy, it is confirmed that many earthbenders who lived in the Fire Nation colonies were absolutely loyal to the Fire Nation and even willing to fight the Earth Kingdom Army for the Fire Nation.