In Abrahamic faiths they both are different which is weird cuz that would mean the Abrahamic God didn't create everything.
A celestial being who out of ego turns evil and wreaks havoc on everything yet in the chapter of Job, God and Satan who couldn't stand each other are having fun on the miseries of his devotee.
Also, in the primary stages of the old testament, Satan remained as a term without any human form. The term simply meant rebel or adversary.
In Hinduism, Devil, demons, humans, celestial beings, animals, plants, insects and the most abominable beings in the cosmos are but manifestations of Krishna.
In agnostic Chinese philosophies, both are two complimentary forces without a physical representation that keeps the other in balance.
In some philosophies like Buddhism, they are two perceptions of the human mind. The devil represents anxiety, greed, fear of education, ignorance, envy and arrogance while the Godly aspects are tranquility, humility, equanimity, submission and devotion towards education of all sorts, generous and humility.
Generally I take the Hindu, buddhist and ancient Chinese philosophical explanations as I highly doubt that anything could exist without the permission by the supreme.