Satan - Just doing his job?

Satan, as a personal name, is rarely found in the Old Testament. Where the name "Satan" is found, it is usually "The Satan" in the Hebrew, even though it is usually translated as simply "Satan". The one time it is used as a personal name, it may be referring to God. Mike Heiser explains the details in his post, The Absence of Satan in the Old Testament. He concludes:

Basically, “the satan” in Job is an officer of the divine council (sort of like a prosecutor). His job is to “run to and fro throughout the earth” to see who is and who is not obeying Yahweh. When he finds someone who isn’t and is therefore under Yahweh’s wrath, he “accuses” that person. This is what we see in Job — and it actually has a distinct New Testament flavor. (We also see it in Zechariah 3). But the point here is that this satan is not evil; he’s doing his job.

So one of "The Satan's" characteristics is to test people's faithfulness We see this not only in Job but also a similar account in the Book of Jubilees when Mastema (who is equated with the personal name, Satan), requests a 10th of the demons to test mankind:

And the chief of the spirits, Mastêmâ, came and said: "Lord, Creator, let some of them remain before me, and let them hearken to my voice, and do all that I shall say unto them; for if some of them are not left to me, I shall not be able to execute the power of my will on the sons of men; for these are for corruption and leading astray before my judgment, for great is the wickedness of the sons of men." And He said: "Let the tenth part of them remain before him, and let nine parts descend into the place of condemnation." And one of us He commanded that we should teach Noah all their medicines; for He knew that they would not walk in uprightness, nor strive in righteousness. And we did according to all His words: all the malignant evil ones we bound in the place of condemnation, and a tenth part of them we left that they might be subject before Satan on the earth.
- The Book of Jubilees 10:8-11

The Book of Jubilees also speaks of the sacrifice of Isaac as being a test from Mestema:

And the prince Mastêmâ came and said before God, "Behold, Abraham loveth Isaac his son, and he delighteth in him above all things else; bid him offer him as a burnt-offering on the altar, and Thou wilt see if he will do this command, and Thou wilt know if he is faithful in everything wherein Thou dost try him." . And the Lord knew that Abraham was faithful in all his afflictions; for He had tried him through his country and with famine, and had tried him with the wealth of kings, and had tried him again through his wife, when she was torn (from him), and with circumcision, and had tried him through Ishmael and Hagar, his maid-servant, when he sent them away. And in everything wherein He had tried him, he was found faithful, and his soul was not impatient, and he was not slow to act; for he was faithful and a lover of the Lord. And God said to him, "Abraham, Abraham"; and he said, "Behold, (here) am I."

And He said, "Take thy beloved son whom thou lovest, (even) Isaac, and go unto the high country, and offer him on one of the mountains which I will point out unto thee." And he rose early in the morning and saddled his ass, and took his two young men with him, and Isaac his son, and clave the wood of the burnt-offering, and he went to the place on the third day, and he saw the place afar off. And he came to a well of water, and he said to his young men, "Abide ye here with the ass, and I and the lad shall go (yonder), and when we have worshipped we shall come again to you." And he took the wood of the burnt-offering and laid it on Isaac his son, and he took in his hand the fire and the knife, and they went both of them together to that place. And Isaac said to his father, "Father"; and he said, "Here am I, my son." And he said unto him, "Behold the fire, and the knife, and the wood; but where is the sheep for the burnt-offering, father?" And he said, "God will provide for himself a sheep for a burnt-offering, my son." And he drew near to the place of the mount of God.

And he built an altar, and he placed the wood on the altar, and bound Isaac his son, and placed him on the wood which was upon the altar, and stretched forth his hand to take the knife to slay Isaac his son. And I stood before him, and before the prince of the Mastêmâ, and the Lord said, "Bid him not to lay his hand on the lad, nor to do anything to him, for I have shown that he feareth the Lord." And I called to him from heaven, and said unto him: "Abraham, Abraham"; and he was terrified and said: "Behold, (here) am I." And I said unto him: "Lay not thy hand upon the lad, neither do thou anything to him; for now I have shown that thou fearest the Lord, and hast not withheld thy son, thy first-born son, from me." And the prince of the Mastêmâ was put to shame; and Abraham lifted up his eyes and looked, and, behold, a single ram caught . . . by his horns, and Abraham went and took the ram and offered it for a burnt-offering in the stead of his son. - Book of Jubilees 16:16-18:12

Again, another example of testing is the garden of Eden when the serpent tempts Eve to eat the fruit of the tree of the knowledge of good and evil. The serpent is not necessarily being morally evil but is testing for the purposes of God.

And again, another example of Satan testing, is when he tested Jesus during his 40 days in the desert.

More Than One Satan

The term satan (not used as a personal name), is a title that can be applied to more that one being.

And I heard the fourth voice fending off the Satans and forbidding them to come before the Lord of Spirits to accuse them who dwell on the earth.
- Enoch 40:7

And a command has gone forth from the presence of the Lord concerning those who dwell on the earth that their ruin is accomplished because they have learnt all the secrets of the angels, and all the violence of the Satans, and all their powers--the most secret ones--and all the power of those who practice sorcery, and the power of witchcraft, and the power of those who make molten images for the whole earth:
- Enoch 65:6

And I saw Him, and He was in the firmament, but He had not changed Himself into their form, and all the angels of the firmament and the Satans saw Him and they worshipped.
- The Ascension of Isaiah 11:23

Another characteristic of a "satan" is that they are like executioners and bring destruction when God expresses His wrath and judgement.

For I saw all the angels of punishment abiding (there) and preparing all the instruments of Satan. And I asked the angel of peace who went with me: 'For whom are they preparing these instruments?' And he said unto me: 'They prepare these for the kings and the mighty of this earth, that they may thereby be destroyed.
- Enoch 53:3-5

And all their days they will complete and live in peace and in joy, And there will be no Satan nor any evil destroyer;
- Book of Jubilees 23:29

The concept of a "satan" is difficult because we have no real earthly equivalent. When God is referred to as a king, we can grasp that because there have been earthly kings to at least give us a general understanding of what a king is.

Is Satan Evil?

Having said all that, just because Satan is doing his job, doesn't mean he's not morally evil. The translators of the Septuagint translated the term "satan" as "devil" - meaning "slanderer", and it implies Satan(s) falsely accuses.