The king of an underwater nation that has stayed hidden for four centuries, who comes to Wakanda proposing an alliance and explaining what happens if it is refused.
Namor’s people were Yucatec, and in 1571 they took a vibranium-laced herb to survive smallpox brought by colonisers. It saved them and changed them: blue skin, gills, and a life that could no longer be lived on the surface. They built Talokan underwater. His mother took the herb while pregnant, so he was born able to breathe both, with wings at his ankles, and he has been alive ever since.
This is the best villain construction Marvel Studios has managed, because he is not wrong. Two hidden nations built on the same metal, one of which has just revealed itself and made the world start looking. Tenoch Huerta Mejía plays him as someone whose patience is a policy rather than a temperament.