Martin Fowler
Martin Fowler is author of the seminal work on refactoring, Refactoring, and chief scientist for ThoughtWorks, a systems integration and consulting company.Martin started working with software in the early 80's and has written five books on the topic of software development. He's also a very entertaining lecturer, often appearing at software development trade shows.
See: The New Methodology, a paper on lightwight software development methodology
His home page is martinfowler.com