"When Calvin does refer to the origin of the devil and demons, he does so to discredit dualism
and to guard against the accusation of some, that Satan was created by God with his present
evil nature. There is no room, in the theology of Calvin, for the view of Satan being, as it
were, the God of evil and darkness opposed to the God of righteousness and light.

Whilst Calvin may not say much about the origin of the devil, what he does say leaves us in no doubt that Satan was created by God (and is therefore subservient to Him) and that his present evil nature cannot be attributed to God in any way. We are, therefore, to content ourselves, as Calvin puts it, with a ‘brief summary of the nature of devils: they were when first created angels of God, but by degeneration they ruined themselves, and became the instruments of ruin for others.’ 

This alone, Calvin believes, is ‘profitable to know,’ because his is all that can be deduced from Scripture. Where this is ‘plainly taught’ in Scripture as in 2 Pet. 2:4 and Jude 6."

                                                                                                                     -churchsociety.org