So I was thinking one day (yes, it happens sometimes) and I've come to theory to who is Creator of our beloved (or hated) Pathfinder.
And hear and behold it's Pathfinder himself! So let me explain my theory:
Creator (let's call him John) wanted to become immortal, nearly indestructible, etc. Maybe he wanted to be a fighter like Pilots are. But John figured that he isn't fighting type guy, he's an engineer. Than it dawned on him: There are Pilot Simulacrums! Of course John knew he would not be able to get this luxury.
But! He is an Engineer! And as engineer he has access to M.R.V.N units! So he "kidnaps" one of the M.R.V.Ns and he takes it to his workshop. There he repurposes the unit for fighting and he adds grappling hook. Then after he's finished, he somehow (don't ask me how) begins to transfer his mind to this robot.
Unfortunately, M.R.V.Ns are not supposed to contain this huge mass of data,so it overloads and the transfer crashes, killing John in process. Only things that were transfered succesfully are: ability to speak, pure happiness and optimism, and urge to fight.
After some time someone discovers John' dead body and takes him to some other place. They leave the robot where it's lying because they don't have use for it. Then somewhen after the M.R.V.N unit activates.
And here we are meeting Pathfinder. Lost and with no memories whatsoever, only with urge to fight and at the same time looking for his Creator.
(Please note that English is not my first language and I'm writing this on a phone so the editing may be not perfect, but I will fix it when I have a chance.)
Source: https://www.reddit.com/r/apexlegends/comments/f90s1g/creator_of_pathfinder_theory/