What Galileo and Descartes had begun, Isaac Newton polished: By discovering the mathematical principles that grounded everything from falling apples to orbiting moons, planets, and comets, Newton laid the foundations of modern physics. Oh, and he co-invented calculus too. And a new kind of telescope. And more. Some of his achievements are readily filed under G for genius; others simply reveal his complex and all-too-human personality. Here are 14 things that you might not have known about Sir Isaac.

1. Isaac Newton was born prematurely and barely survived his first week on earth.

Newton’s father, also named Isaac Newton, died a few months before young Isaac was born on December 25, 1642 (or January 4, 1643 New Style). When his mother, Hannah, gave birth, the baby was so tiny he wasn’t expected to survive. John Conduitt, who would later marry Newton’s niece, recounted Newton’s claim that “when he was born, he was so little they could put him into a quart pot.”

2. Young Isaac was bullied at school—and fought back.

As a youngster, Newton attended the King’s School, the local grammar school in Grantham, Lincolnshire (still functioning as a boys school to this day). One day, the school bully kicked Newton in the stomach, prompting Newton to challenge the boy to a fight after class. John Conduitt wrote that “Though Sir Isaac was not so lusty as his antagonist, he had so much more spirit and resolution.” Newton won the fight, which ended with Newton pulling the other boy by the ears, and pushing his face “against the side of the church.” The incident may have kick-started Newton’s academic performance: Before the fight, he was near the bottom of his class; afterward, he rose to be first in the school.

3. The apple probably didn’t hit Newton on the head.

Like the story of Galileo and the Leaning Tower of Pisa, the story of Newton and the Apple has taken on legendary proportions. Lazing in the garden of his boyhood home, Newton saw an apple fall to the ground; in contemplating its fall, he also thought about the Moon moving in its orbit around the Earth, eventually deducing that the same force—gravity—was the cause of both. As he recalled later, he “began to think of gravity as extending to the orb of the moon.” Historians suggest that the apple story, which Newton only told very late in life, should be taken with a grain of salt. And he never claimed it bonked him on the head.

4. Newton was the quintessential absent-minded professor.

As a student and later a professor at Cambridge, Newton had a reputation for being reclusive, and even a bit nasty. He had few close friends, rarely spoke, and sometimes got so caught up in his work that he forgot to eat. On one occasion, when no one turned up for his class, he’s said to have lectured to an empty room. (Some have suggested that Newton was autistic—a claim that has been made about Einstein, too—but such diagnoses are very hard to support based on historical information alone.)

5. Newton’s greatest work almost didn’t see the light of day.

Newton, who shunned the spotlight, was hesitant to publish many of his results. His most important work, on motion and gravity, collected dust in his study for more than two decades, until astronomer Edmond Halley urged him to publish. The resulting volume was finally printed in 1687 under the weighty title Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Though only a select handful could fully comprehend the book’s dense formulas and diagrams, it cemented Newton’s reputation as the greatest scientist of his day.

6. The “shoulders of giants” thing was actually an insult.

You know the quote: “If I have seen further, it is by standing on the shoulders of giants.” It sounds like Newton is giving credit to the great thinkers who came before. In fact, some historians now believe that it was likely intended as a jab at his rival, Robert Hooke, who was short and possibly hunchbacked. But others point out that Newton and Hooke wouldn’t have a falling out for another 10 years.

7. Isaac Newton loved selfies.

In spite of his reclusiveness, Newton had his portrait painted more than a dozen times, especially in the final quarter of his life. As historian Mordechai Feingold wrote, “Only monarchs, and perhaps a few noblemen, surpassed Newton in the number of times they commissioned portraits of themselves.”

8. Newton was interested in a lot more than science.

We remember Newton for his work in physics, astronomy, and mathematics, but his private letters and notebooks show that he was equally interested in alchemy (the attempt to turn metals such as lead into gold) and biblical chronology—including various attempts to predict the date of the Apocalypse. According to historian of science Stephen Snobelen, Newton’s most confident date for the end of the world was 2060—an idea that led to a provocative 2003 BBC TV documentary called Newton: The Dark Heretic.

9. He may have suffered from mercury poisoning.

Newton spent countless hours in his laboratory working on all manner of alchemical experiments. When some of his preserved hair was analyzed in the 1970s, it was found to contain high levels of mercury, arsenic, and other toxins. Some historians believe this partly explains his irritable behavior, and perhaps also a nervous breakdown that he suffered in the 1690s, when he was in his fifties.

10. Newton once stuck a needle in his eye … for science.

OK, not literally in his eye—but Newton recounts how he inserted a bodkin (a long, thin sewing needle) between his eye and the adjacent bone as part of his investigation of vision and color perception. He inserted it “as near to the backside of my eye as I could,” applying pressure so as to distort the eye. The result? “Several white, dark, and colored circles” appeared. Now that’s dedication. (But don’t try it at home.)

11. He was a lackluster politician.

Newton served two terms in the English Parliament, as the representative for Cambridge University. It’s said that he spoke only when he felt a draft, requesting that the window be closed.

12. If you were a counterfeiter, Isaac Newton was your worst enemy.

Late in life, Newton took up a position at the Royal Mint in London, first as Warden and later as Master. He took his duties seriously, tracking down counterfeiters and anyone guilty of “clipping”—illegally hacking the edges off of coins, and melting down the silver for re-use. Newton devoted much energy to hunting down the offenders, becoming 17th-century London’s Dirty Harry. Several ended up at the gallows.

13. Newton only laughed twice.

Or so it was said. According to William Stukeley, the great thinker once loaned an acquaintance a copy of Euclid’s Elements, a weighty treatise on mathematics and geometry. The acquaintance asked Newton of what use the book might be, “upon which Sir Isaac was very merry.”

John Conduitt tells of a second time he laughed, when asked about why he didn’t talk about our own Sun as much as distant stars. Newton replied that it was because “[the Sun] concerned us more” and, as Conduitt described, “laughing added he had said enough for people to know his meaning.” (Sure it was, Isaac.)

14. After Newton, we redefined the word genius.

In Newton’s time, the idea of genius had traditionally been associated with artists and poets. But after the Englishman’s work became widely known, the word took on a broader meaning. As Mordechai Feingold noted, “Largely owing to the towering example of Newton … in the course of the 18th century the concept was redefined.”

A version of this story ran in 2016; it has been updated for 2021.