HaSatan means simply "the enemy"

in Jewish scripture (Tanakh) he acts as a prosecutor in God's heavenly court, testing human faith, notably Job's, rather than being the ultimate evil figure of later Christian theology. While sometimes appearing as an adversary in war or a generic opponent, in Job, HaSatan is a member of God's angelic host, challenging Job's righteousness with God's permission, a role that evolved into the more distinct, malevolent Devil (Diabolos) in later traditions.