A more thorough explanation:

Advocatus diaboli is a term used in Ecclesiastical law. It refers to an official who argues against a person's beatification or canonization.

• When Mother Teresa was being considered for sainthood, there was an advocatus diaboli who argued against her canonization. He presented evidence that challenged her reputation as a miracle worker.
• During the process of beatification for Pope John Paul II, there was an advocatus diaboli who argued that he had not done enough to address the issue of sexual abuse within the Catholic Church.

These examples illustrate how an advocatus diaboli is someone who presents arguments against a person's beatification or canonization. They are tasked with finding evidence that challenges the person's reputation as a holy figure.