Bruce Schneier is a security technologist, educator, and author. He is widely respected and often quoted, having written many important books about some of the most salient issues of our time: privacy in our networked world, encryption, information security.
He knows what he is talking about. He invented, or helped invent, several important cryptographic algorithms. He writes with clarity and insight, explaining complex technology and how it is changing the world.
He is also a blogger. His blog is interesting and informative.