The Devil Dao can be considered one of the major "sides" of the Dao. It is often seen as the opposite of the Righteous Dao, and as such, the cultivators of the two sides typically depise the other side upon first contact. The Devil Dao is like the Righteous Dao, it does not refer to a specific power or law, it simply classifies a cultivator as "overall evil", although the extent of this can be questioned. It is not known how much bad karma is needed to actually be considered a Devil Dao cultivator.
Cultivators turned to Devil Dao, after discovering the existence of the Elder Devil Realm. They established techniques that were similar to the abilities of Elder Devils and even used secret techniques to part the boundaries of the world so that they could use the devilish Qi of the named Elder Devils, greatly increasing their abilities. According to legends, after reaching the Deity Transformation stage, they could ascend to the Elder Devil Realm, instead of the Spirit Realm.