True enough, but thats not the point. Did Satan create itself, or did God create Satan? If God did, then why?
OK. This goes down to systems of law, and how the ancient Hebrews envisaged God's justice.
Broadly speaking, there are two systems of court: the adversarial system and the inquisitorial system. In the adversarial system, the judge is neutral, he hears the case from two advocates, one for, and one against. From their adversarial sparring the facts emerge, and the neutral judge makes a decision. Each side presents the best possible case, no holds barred, for their particular advocacy, the defence or the prosecution. This is the style used in criminal courts in Britain, the US, and elsewhere, the kind of court depicted in courtroom dramas.
In the inquisitorial system, a judge or a panel of judges participate in the fact-finding. The judge is an active inquirer, rather than an arbiter. He questions witnesses, gathers evidence, etc. This is basically the system used in the Grand Jury in the US, but inquisitorial courts are also found in legal systems throughout Europe and other parts of the world. The term doesn't refer to the Inquisition (though it did use an inquisitorial system).
The ancient Hebrews had, more or less, an adversarial system of law, and their imagining of God's means of justice and decision seems to be a reflection of how they practiced their own law. Christians seem to imagine God practicing justice in the inquisitorial fashion, he finds things out for himself, but the ancient Hebrews did not, they saw him as an arbiter in an adversarial sort of system.
The Satan (not just "Satan" - it wasn't a name, but a job title held by an angel appointed to the role) was the one who acted in the role of prosecutor, presenting the best possible case for condemnation of man, and in that capacity he was charged with finding evidence. With the permission of the judge (God) he could carry out tests designed to elicit a response, to make evidence for his case. This is what you see in Job - an angel, appointed to the role of prosecutor (the Satan), is tempting and testing Job to get evidence in order to present a case for his condemnation.