Midrash B"R quoted by Rashi (Genesis.32.30, and similarly Judges.13.18) says that:
"We [angels] have no fixed names; our names change, all depending upon the service we are commanded to carry out as the errand with which we are charged (Genesis Rabbah 78:4)."
In the Book of Job, does this principle apply to Satan also, i.e. it is just a mission any angel could be called on or is he a stand-alone entity/creation?