A few, if any have had such great influence on the IT industry as Martin Fowler. No introduction needed, really!
But here is how Martin Fowler presents him self:
I'm an author, speaker, consultant and general loud-mouth on software development. I concentrate on designing enterprise software - looking at what makes a good design and what practices are needed to come up with good design. I've been a pioneer of various topics around object-oriented technology and agile methods, and written several books including "Refactoring", "UML Distilled", "Patterns of Enterprise Application Architecture", and "NoSQL Distilled". For the last decade I've worked at ThoughtWorks, a really rather good system delivery and consulting firm.
These days I spend my time helping colleagues share what they learned on martinfowler.com