Iroh is former Prince and a retired Fire Nation general. He is the older brother of Firelord Ozai and uncle to Prince Zuko and Princess Azula.
Compared to the rest of his family he is wise, friendly and an easy-going person. He enjoys drinking tea and playing Pai Sho.
He is an extremely powerful Firebending master and one of the few Firebenders capable of generating lightning. Despite his somewhat clumsy and goofy nature, Iroh is a brilliant strategist and a force to be reckoned with.
Iroh was originally voiced by Mako Iwamatsu for Book 1: Water and Book 2: Earth (season 1 and 2).
Sadly Mako died from cancer and a replacement was necessary for the final season of Avatar: The Last Airbender (the episode "Tales of Ba Sing Se" was dedicated in his honor).
Mako's replacement for Book 3: Fire (season 3) was Greg Baldwin.