Mark Russinovich is one of the most knowledgable people in the world when it comes to all things Windows.
www.winternals.com contains a host of useful utilities and countless code examples for doing things that are either explained poorly or not at all in the Microsoft developer's documentation. He has also written or co-written several books on the deep dark internals of how Windows works.
Safe to say he probably knows more about how Windows REALLY works than just about anyone at Microsoft. And up until this announcement, he was an independent software developer.