G'day from the "Land Down Under" and welcome to, as the God-mobsters, etc, and the undecided or somewhat self-important like to call the Hub of Heresy.

If by "humans" you mean the genus Homo, that was a couple million years ago. If you mean the species sapiens, that was about 300,000 years ago. Monotheism is three or four thousand years old at most. So, not "always".

Human invention - yes. Maybe other species as well, depending on one's definition. Our cousins, the chimpanzees, have some ritualistic behaviors that resemble human religious rituals.

For control of others? Not in the sense of unfair oppression of the general population for the selfish gain of an elite class. It has been co-opted and abused in that way undeniably, but if the suggestion is that it was originally devised for, and currently sustained for, that purpose, no. Not according to history and current scientific understanding, which says it evolved as a biocultural counterbalance to certain human instinctive impulses that were incompatible with life in agriculture-based societies, as opposed to hunter/gatherer societies. So - control - yes, but control of everyone's disruptive instincts - not just of "others". And not for selfish gain, but for the reproductive fitness of H.sapiens.

"From the arrival of the earliest humans..."?????

I think for the earliest humans gods stood in as explanations for misunderstood natural phenomena (e.g. thunder and lightening). It probably was not long before someone figured out that they could use people's beliefs to manipulate them. And religion was born.

I've heard of that, a console fit for a god

Earliest humans had an excuse for their primitive explanations.

Welcome aboard the heathen, heretic train!

It is my opinion that god was a human construct to explain natural processes that ignorant early humans did not understand. It is my opinion that religions were a human construct to control others.