Charles Darwin changed the world more than anyone else in human history.
Charles Darwin's Faith and Religious Beliefs
From the link what his future wife wrote:
"I must now tell you what I think of him, first premising that Eliz. thinks pretty nearly the same, as my opinion may not go for much with you. He is the most open, transparent man I ever saw, and every word expresses his real thoughts. He is particularly affectionate and very nice to his father and sisters, and perfectly sweet tempered, and possesses some minor qualities that add particularly to one's happiness, such as not being fastidious, and being humane to animals. We shall live in London, where he is fully occupied with being Secretary to the Geological Society and conducting a publication2 upon the animals of Australia."