American historian extraordinaire Forrest McDonald and his wife Ellen Shapo McDonald have a very solid answer to that question: John Dickinson. Read their whole answer over at The Imaginative Conservative. I don't think there is much question that Dickinson is massively overlooked by most modern historians. Along with Samuel Adams, John Jay and Patrick Henry, Dickinson is out of fashion with the modern age. Part of this has to do with the fact that none of those men every ascended to the presidency. But part of it has to do with the intellectual fads and obsessions of our time. Thus, they are not the subject of serious study for the most part. Yet our Revolution and our constitutional order would have been impossible without those men. The fact that they are overlooked says far more about us than it does about them.
[Cross-posted over at my own blog, Libertas et Memoria.]