What is the most attractive non-physical characteristic someone can have?

To borrow the new age term, an old soul.

There are just people who possess a sort of cynically detached understanding of the world and people. They aren't fired by largely pointless passion or desire, they're intelligent and perceptive enough to generally understand things and emotionally mature enough to generally accept them and they have a way of just sort of gliding through life, maintaining a relatively even keel instead of getting distracted and disconcerted by irrelevancies.

Every single person I've ever known who was like that has been or is special to me.