understanding the devil

Well, after seeing some inconsistencies in the Bible, it is hard to paint a clear picture of the devil, if the devil even is one specified being. It appears to be that the personification of evil occured through literature. The devils personality, appearence, etc varies throughout the different works of literature we have read. I still believe that there is a devil and he is a reflection of all evil and temptation in the world; however, that's about all I'm sure of. How he came into being, whether he works for God, and his appearence/personality seems to vary in differnt texts. I guess its subjective to time period.