Considering Satan is a fiction, I’d say Satan can be whatever you want him to be.
This is probably also true for the Christian God. But let’s assume for the sake of discussion that the Bible is a factual account: the Book of Numbers already refers to the worship of the Semitic god Ba’al in the “ancient” people of Israel. Etymologically speaking, Ba’al is identical to what later became “Beelzebub”, one of the names of Satan; it is reported that the statues of Asherah (the wife of YHWH) and Ba’al were destroyed. Ultimately, according to the Bible, the followers of YHWH waged a “holy war” against the followers of the other gods and declared these gods to be the “Antichrist” by a mere act of speech.
It is not known whether the followers of Ba’al were really less merciful than those who later waged crusades.