There is a narrative of religion in the Islam, that the original religion of Mankind was that of Monotheism, and that over time men added gods (such as heroes representing virtues) to it, changing it from the true natural monotheism to artificial polytheism.
The Arabs of Mecca were upon the Monotheism of Abraham and Ishmael (pbut) until a man called Amr bin Luhayy brought idols with him from the north, the Levant. He saw there literature, architecture and the practice of polytheism. He was impressed and brought polytheism back with him to Mecca, and convinced the people to worship an idol he brought. This faced little resistance and the number of idols worshiped grew to around 360 by the 6th century CE.
Shirk - The Arabic term for worshiping other than God (lit. Association, compare Hebrew "
Shituf"), it is the worst sin man can commit
There is more information on Islam in the
datasheet thread and links to videos.
Merciful Servant has many well edited videos with Muslim lecturers.