I'm obsessed with Charles Darwin.
I love that, as a young man, the guy who would come up with the theory of natural selection was told by his father, "you are the shame of your family, and will never amount to anything." (Or words to that effect, don't quote me!)
And then, off he goes on the 5-year trip around the world in the H.M.S. Beagle, and puzzles over why tortoises on different islands in the same chain, that look otherwise the same, have different shell structures, and why finches on all the islands have so many different behaviors - there's even a "woodpecker" finch!
I love, too, how he sat on his research for twenty years, not wanting to be the man who tells the world, 'well, we thought that we were the be-all and end-all, but it seems that that may not be the case.' He apparently wrote to a colleague, "publishing this theory is akin to publishing a confession of murder." (Again, not sure of exact wording.)
Finally, I love that after his voyage on the Beagle, he hardly left home again, like Dorothy coming back from Oz.