Erebus says:
Oh, maybe that spawns also the question of who built the gates and where he is now?
PAYING 1 TOKEN
Not 'he'...they. The people who created the gate where powerful heroed trying to prevent the destruction of the world. The process to create the gates was taxing and required then to infuse some...sometimes all of their life essence into the gates. That energy is what sustains the connections and allows travel.
Now that the gates are threatened, these great heroes are being reincarnated in PCs, bound to protect the world again as they have done countless times in the past. Sometimes they remember who they are, other times they don't, but they always appear when something threatens the world. It has been ages since the last appearance of a Gate Hero, so the PCs are something special. There is even a quasi religious order that seeks out reincarnated Gate Heroes and invites them to gather and train. Some go, nsome don't. The Order of the Magi believe that they are best suited at training and preparing Gate Heroes, but they can't force the issue because Gate Heroes are to powerful. ((Note: I intend to use the "teacher/leader" definition of Magi...not the "wizard/magic user" per se.)) Gate Heroes come in all forms. Fighters, wizards, farm girls, stable hand, kings and paupers. Just because your soul used to belong to a Gate Hero doesn't mean you are immediately better off than anyone else. I'd also like there to be people who dislike the idea of Gate Heroes. They don't believe they are reincarnated heroes, but actually cause the trouble they claim they exist to fight. The people don't see any problems, then all of a sudden a Gate Hero shows up and bad stuff happens. This isn't everyone, just a large, sometimes very vocal minority.
So the short answer is "The ancient Gate Heroes, and they have returned."
Sorry if answering again so quickly was a breach of protocol, but it was the perfect setup.