God

A god is a superhuman being or spirit worshiped as having power over nature or human fortunes (also known as a deity). They are the central focus of a religion (a system of beliefs and teachings revolving around the belief in and worship of a superhuman being). In some accounts they are also the creator (or creators of the world and everything in it - in-universe in the case of some fictional universes).

In real-life there are various religions and (as of the the time this was written) the majority of the world's population are religious, and even some non-religious people believe in the existence of a god or gods. The most popular (and arguably the most credible) are the Abrahamic faiths Christianity Judaism and Islam who worship God as the supreme creator and ruler of the universe. Religions go back to the beginning of human history (and even further, as hotly debated as that is).

As a person's religious beliefs are their most important beliefs (regarding the non-religious, their non-religious views are still their most important beliefs), and this in turn determines the big things such as the purpose of life and what happens to people after they die, this has led to a lot of arguments and even in some cases wars (though not as many as some people claim). As a result of the massive influence in real-life (which is undeniable regardless of anyone's personal views and beliefs on the subject) and the various views on the subject, the subject of God, a god or gods often crops up in fiction.