What is the word for someone who compulsively compares themselves to others.

I posted this in TOMT, and specified after the initial post that a narcissist is not the word I'm looking for. A narcissist is at the high end of the self-esteem spectrum, and compares him/herself to others as superior, but what about a person who always compares themselves as inferior?

This phenomenon seems to be just as common as narcissism! A word for this must exist!