> Alignment is an essential part of the nature of celestials and fiends.
Generally, evil alignments are for villains and monsters.
A devil does not choose to be lawful evil, and it doesn't tend toward lawful evil, but rather it is lawful evil in its essence. If it somehow ceased to be lawful evil, it would cease to be a devil.
— Alignment in the Multiverse, Player's Handbook, pg. 122