for Aquila's sake,
1Peter 5:8 Be sober, be vigilant; because your adversary
the devil, as a roaring lion, walketh about, seeking whom
he may devour:
the underlined word "the" is a definite article, in this sentence "the" is used as a function word to indicate that the following noun is a unique or particular member of its class.
the underlined word "he" in this sentence is a pronoun and is used as a substitute for the word "devil" whose referents are understood in context.
In this scripture the devil is referred to as a single individual. (Although there can be many devils).