Satan is generally thought of as a mythological being that makes people believe that the Earth is round (an irregular oblate spheroid) rather than flat and that the Earth is 4.54 Billion years old instead of 7k years old. Satan is also the one who signs the paychecks to the many of the members of the GDC as they shill for him and NASA by being covert members of the Illuminati infiltrating G+ and YouTube to spread "Evilution" and the belief that there is no God.

In Islam, Satan is known as "Shaitan" but for most of us Satan inhabits the body of our mothers in law or the body of many irresponsible husbands to their families (per wives' complaints).

(I'll write the history of the devil sometimes this week as this is a subject I know very well-leaned.)