In the three big monotheistic religions the creator is known as God. Christianity, Islam and Judaism are the most populated religions around the world. While they all have differing beliefs, they all do believe in God. This is a quick overview of those three religions and how God came to be.
The idea of one God began with Judaism. They believe that God, also known as G-d or YHWH, spoke to Moses and provided the Torah. Moses wrote down everything that God told him and provided the Torah for all Jewish followers. God then told Abraham that all of his descendents would become a nation (Israel) and that they all must love the world as He does. Abraham had to worship and pray to God, referred to as Yahweh, in order for this to happen. They made an agreement, a covenant, that would make both Yahweh and the Jewish people happy. Judaism is the smallest of the three monotheistic religions, but it is the oldest and also the root of the other two prominent monotheistic religions.
Later the birth of Jesus Christ, who was a Jew himself, through the virgin Mary added an additional monotheistic religion. Christianity is the belief that God sent down Jesus to save all of his people from their sins. As Jesus ascended to heaven he told the people about the holy spirit which would act as a way for them to have God around them at all times. So Christians believe that God is the father, the son, and the holy spirit. Jesus saved all of his followers by being crucified on the cross, which is now a major symbol of the religion. In order to be saved believers must confess their belief which is typically done through some sort of baptism which is an outward expression of faith in Jesus.
Gabriel the angel spoke to Muhammad which began the religion of Islam. The followers of Islam believe that God, known as Allah, spoke to Muhammad to bring back the one true religion and worship the one single God. These words were written down and known to be the Quran which is thought of as the words of Allah and not the people. Islamic followers strongly emphasize and believe in monotheism. They also strongly encourage praying five times a day and giving to those who are in need. Islam acknowledges in their text both Jesus and Abraham, but they believe that they were only prophets.
All three have laws and individual beliefs, yet they agree that there is only one God. He is represented very differently in all three religions as well as other monotheistic religions that are less populated. Even though all followers of the three religions have different stories they all agree that they cannot have a picture of God because they do not accurately know what he looks like. He is often depicted as a hand when He is shown, but no face or figure is drawn out. God has a long history that can be traced back through many different religions; I encourage you to go and do some more research on your own to see what your belief is.