In Marvel comics, Namor is the half-human ruler of Atlantis, but presumably Coogler and his team decided to make some revisions so as to differentiate Namor from Jason Momoa's Aquaman in the DC / Warner film. They needn't have worried too much about the comparison. The seaweedy realm of Talokan is more beautiful and well-realised than anything in Aquaman, and Namor's tragic origin story, which dates back to 16th-Century Yucatan, is more interesting.
