A polymath is defined as a person of great or varied learning.
The first person that comes to my mind when I hear this word is Ben Franklin – because the word evokes for me specifically a person who’s knowledge is both deep and varied – in essence a generalist. One might say that Franklin “dabbled” in everything – but in fact “dabbled” seems an inappropriate word, since it implies someone who never looks beyond the surface.
Wikipedia lists similar terms such as Renaissance Man, Generalist, and Homo universalis and also includes a list of noted polymaths including Imhotep, Aristotle, Cicero, Leonardo da Vinci, Galileo Galilei, Isaac Newton, Thomas Jefferson, and of course Ben Franklin. Good company to aspire to, I think!