This may be the most important question that man has ever asked. It also has one of the most widely disputed answers. Most of the numerous answers out there fall into three categories.
Most people know of the Greek gods.
Zeus, Aphrodite, Mercury and Venus are all very well known gods. Any person who believed in these gods would be a polytheist, basically someone who believes in multiple gods. These gods had flaws and none of them were perfect. The general trend in philosophy and religion has been that of reducing the number of gods or godlike beings. This brings us from polytheism to dualism.