From Satan Service
Devils in general, or spirits perceived to be maleficent or intending some human beings harm, have been been described during the entirety of recorded human history. The terms by which they were recorded of course varied, and it wasn't always the case that these were separated out as a species so much as treated like cooperative and antagonistic individuals within a given milieu. At times, devils or demons were characterized as waging a titanic struggle in the heavens (e.g. the asuras vs. the devas in Persian vs Indian cultures, respectively, or titans vs. gods among Greeks). And at times the demonic was identified as associated with the Underworld in comparison to the terran plane or the heavenly abode.
In some religions, such as Christianity and Islam, certain devils are pitted against their focal deity and affixed with a title 'The Devil', and this usually implies the leader of the titanic horde, often described as the root of all posited moral problems, evils, etc., in the universe.