Initiator
The commandment came from God, He initiates and instigates the accuser on all accounts. The accusers brings a very weak case against Job but it was sufficient for God because Job was guilty of self-righteousness
God initiates chapter 1
“And the Lord said to Satan, “Have you considered my servant Job, that there is none like him on the earth, a blameless and upright man, who fears God and turns away from evil?””
Job 1:8
God initiates chapter 2
“And the Lord said to Satan, “Have you considered my servant Job, that there is none like him on the earth, a blameless and upright man, who fears God and turns away from evil? He still holds fast his integrity, although you incited me against him to destroy him without reason.””
Job 2:3
In the second chapter we can see God showing the Accuser that his argument was not only weak but wrong, but Job was still righteous in his own eyes. Never does God in the Hebrew say that Job is righteous only blameless and upright but never righteous
Executer
The Accuser carried out the plan in both chapters he brings the judgment issued from the divine counsel, scene that is seen throughout OT, God meeting with heavenly beings to execute His will and to have counsel meetings
Source
The source was Job’s self-righteousness which is pride and destruction follows prides.
“Pride goes before destruction, and a haughty spirit before a fall.”
Proverbs 16:18
What Job experienced was nothing short of destruction
“So these three men ceased to answer Job, because he was righteous in his own eyes.”
Job 32:1
Self-righteousness is a form of pride because righteousness belongs to God alone. Righteousness can only even be imputed to man, never earned
“I will get my knowledge from afar and ascribe righteousness to my Maker.”
Job 36:3
Conclusion
Ultimately God in His grace decided not to let Job pass into eternity without being given a chance to repent. Unfortunately the sin of self-righteousness is so subtle and strong that it takes a very large amount of judgment to be carried out for a man to realize the error of his way. Job brought it upon himself, God had to make a judgment call and the Accuser merely executed.