Avatar: The Last Airbender

The Avatar is an international arbiter whose duty is to maintain harmony among the four nations, and act as a mediator between humans and spirits. When the Avatar dies, their spirit is reincarnated in a new body, who will be born to parents in the next nation in a set order known as the Avatar cycle: Fire, Air, Water, and Earth. By tradition, the new Avatar will travel the world to learn all four bending arts, after which they will begin in earnest their role as global peacekeeper. The Avatar can enter a condition known as the "Avatar State", in which they temporarily gain the skills and knowledge of all their past incarnations. Although this is when they are at their most powerful, if the Avatar was ever killed while in the Avatar State, the reincarnation cycle would be broken and the Avatar would cease to exist.