Original: The character, created by Michael Dante DiMartino and Bryan Konietzko, was voiced by Mako in the first and second seasons, but after Mako's death of esophageal cancer, Iroh was voiced by Greg Baldwin in the third season.
Simplified: The character and series were created by Michael Dante DiMartino and Bryan Konietzko. Iroh is voiced by Mako in seasons 1 and 2, Greg Baldwin onwards.