It was the people who deviated from the right path and sometimes they started worshiping stars and sun and moon and other natural phenomena and sometimes they carved the shapes of their beloved dead ones and started worshiping them as gods. The question frequently asked is, why did they people deviated from ALLAH if HE is true GOD. The reason is very simple, whenever men stopped understanding and striving and relied on their own limited logic and knowledge, they deviated from the path of ALLAH.
But ALLAH swt sent towards HIS people, 1,24000 messengers who took the task of preaching and keeping people on the way of ALLAH. Some followed them while some did not. So this process of belief and disbelief kept on going till to date. Even today we see many people from many different cults and religions each based on their own ideology which they can defend or pretend to defend with their logic.
What could be the status of that god which can be defined and imagined by human mind? Certainly, such a god is nothing. GOD is one who is beyond our imaginations and our limited scope of thinking and knowledge.
Regarding the islam before Muhammad s.a.w.w , below are given two verse of Quran as proof.
Al Quran [004:163]
We have sent thee inspiration, as We sent it to Noah and the Messengers after him: we sent inspiration to Abraham, Isma'il, Isaac, Jacob and the Tribes, to Jesus, Job, Jonah, Aaron, and solomon, and to David We gave the Psalms.
In the verse above, ALLAH swt tells us about those prophets who were given divine inspiration. These prophets were given the divine guidance in written form or reveled form so that they could guide their nations with the divine word.
Al Quran [004:164]
Of some apostles We have already told thee the story; of others We have not;- and to Moses God spoke direct;-
The prophets about who are told are few and the prophets about who we are not told and very many. Why we are not told about other, there must be some wisdom behind it. We should be content with what we know. To get the knowledge beyond our scope will not help us but will only cause us harm, the harm of disbelief because there are many question which have no answers in any religion.