Ockham's razor is named after William from the village of Ockham who propounded it. However it is often written Occam. It is not at all clear which is correct, in those days spelling was not nearly so standardised.
The reason that Occam's razor is needed is that it is always possible to come up with ever more bizarre theories to explain any behaviour of the world.
Is the moon pushed around by the beat of invisible, intangible faeries wings? Doubtful, but it may be difficult or even impossible to disprove. Or is it this newfangled gravity thing? Or does the earth create a suction? How can we prove it? We often can't.
But we need somewhere to stand to compare things against. Otherwise all of science become strictly a matter of opinion. That's what The Razor provides us.
In fact, Ockham's razor is way of building what statisticians call a "normal hypothesis"- the default theory that any new theory must be experimentally compared against in order to prove its mettle.
Contrary to popular belief Scientists or anyone else are welcome to believe whatever they want, but people in science will generally expect you to compare your theory experimentally against a reasonable Normal Hypothesis (see Standard Model); and try to disprove the normal hypothesis.
Interestingly, Ockham's razor may be applied to religion, and it generally states that there is no God. However, that does not disprove the existence of God, only that God cannot be the default scientific theory without direct evidence (God is a very complex concept, omnipotent, omniscient etc.); if you're religious, that's what faith is for.
Ockhams razor, or some similar concept, is both subtle but vital to science. It is practically the definition of Science.