What trait do you admire most in a co-worker?

One of my co-workers is unquestionably the most gregarious person I know. He can and often does talk with anyone. We were at an event together and, as we were supposedly heading out the door, he struck up conversations with a) my old college advisor, whom I hadn't spoken to in 33 years, b) the chancellor of the university and c) the executive editor of The New York Times. Me, on my own, would have been long gone — if it had been up to me, I wouldn't have gone at all.