He is a priest who also serves as the King Fernando's adviser; however, he is also an evil Makai Alchemist who is very ambitious, greedy, and manipulative. He uses "Horrors" to do his dirty works and whereby he frames other Makai alchemist, warlocks, witches, and knights for the famine, pestilence, and other misfortunes that has come to the kingdom—that he himself caused. He has manipulated the king into declaring a witch hunt all over the kingdom where a lot of magic users and Makai knights where either, imprisoned, killed, tortured, or burned to the stakes. Later on is the series, it is revealed that Mendoza was cursed and exiled from the Makai for proposing that the Makai rule humanity instead of protect it. This led his master to swiftly exile him and place a curse onto him that covered his entire body in scars and sores that would curse future generations of his lineage. (Source: Anime+, edited)