Devil Slayers (滅悪魔導士 Debiru Sureiyā) are people who use Devil Slayer Magic.
Also known as Exorcist Mages (悪魔祓いの魔導士 Akumaharai no Madōshi), Devil Slayers are people that utilize Devil Slayer Magic. Like Dragon Slayers and God Slayers, Devil Slayers can also become immune to the effects of their respective element and can even eat it to replenish their strength. It appears that Devil Slayers can manipulate their own body to some degree, allowing them to change the color of their irises and summon black markings across their body at will. The markings seem to help them resist the effects of Curses (including the self-described "Ultimate Curse" Memento Mori) by turning part of the user's body into that of a Demon. These Mages also have the ability to analyze the body composition of Demons by merely looking at them.
Those who utilize Devil Slayer Magic are stated to gradually lose their sanity, becoming increasingly unstable and eventually going berserk. This was demonstrated when Gray not only fought Natsu, but actually tried to kill his friend.