Both Jesus and Paul (an educated man and author of several letters to early Christians) spoke of someone other than our Creator, our Father--Jehovah, as being “the ruler of the world” and the “god of this system of things.” In speaking to disbelieving leaders of his nation, Jesus identified this one as being the Devil.
For some, this is a very hard concept to wrap their minds around. Did God (Jehovah) give up on mankind? Did he give up his authority, rulership or interest over the earth and mankind? The answer is no. God still very much considers the earth as his creation, his possession, and his dominion. How then, can anyone but Jehovah be “the ruler of the world”? The answer lies in understanding that the aforementioned scriptures define “world” and “system of things” as referring to the masses alienated from God because of their own choice to reject not only his rulership, but his direction and guidance regarding what is proper both in our relationship with him and with others.
Jesus identified Satan the Devil as being a father to anyone who is disobedient in a manner like Satan. Although in context Jesus was talking to religious leaders who were blatant liars and having a murderous heart, he made a very sobering claim that affects all people--He said that if we are not actively supporting his interests, he considers it the same as working against his interests. Satan is god to all such ones because, like himself, they follow a course of choosing an independent course in life--in complete disregard of the fact that they owe their very lives to their creator. How can we individually ensure we are not among those type of people? That is beyond the scope of this article. In the meantime, here is more information explaining how Jehovah has not given up his authority over the earth and mankind.