In 1587, the Catholic Church established the office of Promoter of the Faith, which was commonly known as the Devil’s Advocate. This position was occupied by a canon lawyer who was charged with presenting the case against a candidate for sainthood. (The case for sainthood was presented by the Promoter of the Cause, or God’s Advocate.)
In 1983, Pope John Paul II changed the canonization process from adversarial to inquisitorial. The job of Devil’s Advocate was abolished and a new official called the Promoter of Justice was created to investigate and decide on holiness claims. As one might expect, this procedural reform led to a sharp increase in the number of saints. (About 500 during John Paul II’s reign as opposed to about 100 in the previous eighty years.)
My conclusion: Satan is an underserved client. I leave it to legal ethicists to determine whether he is entitled to pro bono assistance.