There is no evidence of such a demon as a real, historically documented presence -- if deals with demons were as effective as they were reputed to be during the Middle Ages, and also as relatively easy to make, the face of European history would look different and so I suspect would the present day. Medieval people took these dealings with devils quite seriously, but whether the devils they described in writings about such contracts are real is a religious/occult matter suited to a different subreddit, not a question of historical fact. Are you interested in how medieval people conceptualized deals and contracts with supernatural powers, or early instances of this motif in medieval literature and folklore?