Once long ago, a creature evolved. Just as man was to an amobea this creature was to man. It only had to occur once, for this creature could see everything and go everywhere. No one really knows their beginning except for may them. I use a plural because most people who are knowledgable enough to know of them believe there to be more then one.
What is known is that they do not take part in the petty dealings of mankind or even the universe. Some speculate that they have no value in even their own life, that they are just a physical representation of the universe’s memory; that they would watch themselves get shot just to record the information.
Although they are far from omnipotent, they are not far from omniscient.