Richard Feynman
If one person has showed me the fun of learning, it's the physicist, lock-breaker, bongo-player, and artist (among others) noted above. I first stumbled across him in a series of short youtube clips about a decade or so ago (mid 2000s) and though I didn't know it at the time, they began a series of changes in my mindset that has shifted virtually everything about me in a more positive direction. I bring it up now only because I came across a full-length cut of the original videos I watched and I want as many people as possible to see it and experience the sheer joy of thinking about the world in new ways that Feynman seems to convey.
If you watched and enjoyed the video linked above (or didn't), I highly recommend reading the book “Surely You're Joking, Mr. Feynman!”. He has an infectious way of thinking about the world.
2020-12 (Updated link to 'HD' version)