God may have been intentionally invented as a means to…

God may have been intentionally invented as a means to control the masses.

Example would be religion that incorporates caste system.
There clearly is reason to do so, as people tend to obey commands with absolute (divine) justification
Religious institutions have historically held power over masses.
Looking at world religions through the eyes of cultural evolution, it is clear that the more controlling (and "jealous") gods / religions tend to spread further than the more lax belief systems.

Believers appear to be serious about claiming his/her/their existence.
This is highly unlikely as all societies have adopted religion in some form and they are unlikely to all have coincidentally fallen prey to manipulative governance.
A ruler (ruling class) diminishes their own power, rights, and authority by inventing a deity whose power supercedes their own.
This propose implies a too complex and direct awareness of the human communication laws. It's widely more probable that the 'centralized' concept of mediator between humanity and divinity came after the birth of the concept of God and its spread inside the communities.
This does not address whether He exists or not; maybe evolutionary theory was developed by atheists to 'control' Christians, but its validity as a theory is not affected by this.
The concept of God is intuitive and resides in the psychological commons. Religion, on the other hand, is an invention to portray a certain understanding of God and it is a human creation.
In many communist countries, God is banned to control the masses. So the concept of an absence of God must have been intentionally invented by humans.