In Doctor Faustus, Wagner is Faustus's servant and student. Wily, cunning, and more than a little devious, he shares his master's desire to get more out of life. But unlike his master, Wagner doesn't feel the need to take such drastic steps as selling his soul to the devil to get what he wants out of life. He simply observes Faustus to work out how to exploit the forces of darkness for his own ends.
Having decided that he wants a servant of his own, Wagner conjures up a couple of demons to spook his would-be apprentice, Robin, into signing the deal that will make Wagner his master. Although dabbling with magic is potentially dangerous, Wagner doesn't appear to suffer any serious consequences. In fact, not only does he end up with his very own servant, he becomes the beneficiary of a generous portion of his master's wealth by the end of the play.
This is entirely in keeping with the bizarre world that Doctor Faustus depicts. In signing his soul to the devil, Faustus is challenging the natural order of things. And Wagner, a great admirer of his master, follows suit, challenging the social hierarchy by turning himself into a master—complete with substantial wealth and his very own servant.