"The Four are equally obvious and secretive, and while you will always know them when you meet, we usually know little about the Four. Where they came from, who they were; with some notable exceptions, like Lady Ghelined."
— Farganah, historian
How long it took them to make the world is unknown, and theories are wildly debated among scientists. Just as unknown is the species of the First Four, but there is a traditional canon assuming the Axeswinger to be a rhu'khach, the Swordmaster a beja, the Spearbearer a raganaj, and the bowarcher an elf. Since nobody today knows the shape of a rhu'khach anymore, the Axeswinger is commonly depicted as either a tall human or a fantastic creature assembled from different sources.
This is how Kitaians assume the world was made. Because the Four are the primordial beings resembling gods in Genius Loci - making them kinda important -, I come back to them time and again. Being one of The Four is a title, not a trait; they're not reborn, but new Four are chosen every cycle.