Satan is a character that appears in the belief systems of many religions, including Christianity and Islam. In Judaism "satan" is not a sentient being but a metaphor for the evil inclination – the yetzer hara – that exists in every person and tempts us to do wrong.
Satan As A Metaphor for the Yetzer HaRa
The Hebrew word "satan" literally means "adversary" and in Jewish thought one of the things we struggle against every day is the "evil inclination," also known as the yetzer hara. The yetzer hara is not a force or a being, but rather refers to mankind's innate capacity for doing evil in the world. Using the term satan to describe this impulse is not very common though. (The "good inclination" is called the yetzer hatov.)
References to "satan" can be found in some Orthodox and Conservative prayer books, but they are viewed as symbolic descriptions of one aspect of mankind's nature.
References to Satan in the Hebrew Bible
Satan appears as a proper character only once in the Hebrew Bible. In the Book of Job he is depicted as an angel who mocks the piety of a righteous man named Job. He tells God that the only reason Job is so religious is because God has given him a life filled with blessings. "But lay Your hand upon all that he has, and he will curse You to Your face" (Job 1:11). God accepts Satan’s wager and allows Satan to rain all manner of misfortune upon Job: his sons and daughters die, he loses his fortune, he is afflicted with painful boils. Yet even though people tell Job to curse God, he refuses. Throughout the book Job demands that God tell him why all of things horrible things are happening to him but God does not answer until chapter 38. "Where were you when I established the world?" God asks Job, "Tell me, if you know so much" (Job 38:3-4). Job is humbled and admits that he has spoken of things he does not understand.
The Book of Job grapples with the difficult question of why God allows evil in the world. It is the only book in the Hebrew Bible that mentions "satan" as a sentient being. The idea of satan has a being with dominion over a metaphysical realm never caught on in Judaism. Judaism is so strictly monotheistic that the rabbis resisted the temptation to characterize anyone other than God with authority. Rather, God is the Creator of both good and evil and it is up to mankind to choose which path they will follow.