Sir Isaac Newton is considered to be one of greatest thinkers that ever lived. The father of modern physics studied alchemy, optics, gravity, and numerous aspects of science and mathematics over the course of his life, making few friends and demonstrating some pretty odd personality characteristics in the process.
Devout yet vengeful, brilliant yet anti-social, dedicated yet lazy - Newton was full of his share of dualities and quirks. Experiences from his youth shaped his personality into that of a temperamental and paranoid man who wasn't afraid to trash-talk his competitors and embellish his own contributions when it suited him. However, there are many facts about Sir Isaac Newton that aren't well-known - some are sad, while others are downright strange.
Newton had a substantial mental breakdown in 1678, in large part due to the immense stress brought on by the controversies surrounding his work. His mother died the following year, at which point he became even more isolated and dove deeper into his research. In 1693, he experienced yet another breakdown very similar to the one he experienced years earlier. Newton was embarrassed by his battle with mental health - a lifelong struggle by all accounts - which may have been due to depression or a form of bipolar disorder.
Newton began publishing his research on light, color, and motion, with his first presentation being at the Royal Society of London in 1672. His ideas about light contradicted those of noted scientist and head of the Royal Society, Robert Hooke, earning Newton immediate criticism. Newton argued that light was made up of particles while Hooke believed it was a wave - and because Hooke had more academic clout at the time, a bitter rivalry developed. Hooke went so far as to convince fellow scientists that Newton was wrong.
Then, in 1675, Newton published another paper that drew even greater criticism; however, this time he was being accused of plagiarizing Hooke's ideas about the relationship between planets and the sun. Hooke, for his part, did have his own ideas about gravitation and the way that planets were attracted to the sun, but he never articulated a theory. The claims of plagiarism were unfounded, but it was still enough to drive Newton into a fit of rage in which he vowed to quit the Royal Society and never publish again.
Newton never seemed all that interested in women and never married. There is no evidence of him ever having been in a relationship of any kind, which has prompted some people to suggest that Newton remained a virgin throughout his life. His bad temper and aversion to people may have also played a part.
On the other hard, though, it's has also been suggested that Newton took some sort of vow of celibacy early on, to which he remained loyal until his death at the age of 84.
In addition to confessing that he had wished for the death of his stepfather, Newton listed 48 of his most offensive sins at the age of 19. He recounted numerous violations of working on Sundays and not honoring God, but also of lying, punching his sister, and having unclean thoughts.
He also wrote about conducting experiments on himself, most notably sticking a needle in his own eye while he researched optics. He also stared into the sun for extended lengths of time in order to experience changes to his vision.