Question about verbal/emotional abuse?

I have heard it said that people who are verbally or emotionally abusive - control freaks, etc. are suffering from a psychological disorder. If that is the case, what type of disorder would it be clified as? Perhaps narcissism? What is the best way to try to help someone like this (an otherwise amazing person) who has no idea how awful they can be? Ive thought about writing a letter because this particular individual does NOT like to listen or be told that he is wrong (obviously an aspect of the disorder)...but im afraid that any sort of criticism will only fuel the fire so to speak? Any insights or suggestions will be appreciated, thank you.