After giving our readers two days to reflect on the first list of key scientists, we now unveil part two. Originally, the full list was meant to cover 20 names, and while some from the initial comments are missing here, don’t worry—the third installment is on its way, continuing our celebration of history’s most significant scientific thinkers.
20. Johannes Kepler 1571 – 1630

“I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses.”
Kepler, a German mathematician and astronomer, played a pivotal role in the scientific revolution of the 17th century. He is most famous for the laws of planetary motion that bear his name, which were later built upon by other astronomers based on his works, such as *Astronomia nova*, *Harmonices Mundi*, and *Epitome of Copernican Astronomy*. These laws also laid the groundwork for Isaac Newton’s theory of universal gravitation. Kepler blended religious thought with his scientific endeavors, driven by the belief that God created the universe in a rational way that could be understood through reason. He referred to his astronomy as “celestial physics,” an exploration of Aristotle’s *Metaphysics*, and a complement to Aristotle’s *On the Heavens*, redefining the ancient approach to physical cosmology by positioning astronomy within the realm of universal mathematical physics.
19. B.F. Skinner 1904 – 1990

“A person who has been punished is not thereby simply less inclined to behave in a given way; at best, he learns how to avoid punishment.”
B. F. Skinner, an American psychologist and inventor, developed the operant conditioning chamber and created the philosophy of science known as Radical Behaviourism. He also established his own field of experimental research psychology, called the experimental analysis of behaviour. His work, *Verbal Behaviour*, which has gained significant experimental and applied interest in recent years, represents a major culmination of his studies on human behavior. In a recent survey, Skinner was named the most influential psychologist of the 20th century, surpassing even Sigmund Freud.
18. Dmitri Mendeleev 1834 – 1907

“Pleasures flit by – they are only for yourself; work leaves a mark of long-lasting joy, work is for others.”
Mendeleev, a Russian chemist and inventor, is best known for creating the first version of the periodic table of elements. Through his table, he was able to predict the properties of elements that had not yet been discovered.
17. Gottfried Leibniz 1646 – 1716

“Everything that is possible demands to exist”
Gottfried Leibniz, a German scientist and mathematician, independently developed infinitesimal calculus, an achievement that he shared with Newton, and his notation remains the standard to this day. He also invented the binary system, which is the foundation of nearly all modern computer systems. Along with René Descartes and Baruch Spinoza, Leibniz was one of the leading 17th-century rationalists. His work extended far beyond mathematics, contributing significantly to physics, technology, and anticipating concepts in fields like biology, medicine, geology, probability theory, psychology, linguistics, and information science. Leibniz also wrote extensively on politics, law, ethics, theology, history, and philology, as well as some occasional poetry. His extensive contributions across these diverse areas can be found in journals, thousands of letters, and unpublished manuscripts. To this day, a complete edition of his works has not been published.
16. Thomas Edison 1847 – 1931

“Genius is one percent inspiration and ninety-nine percent perspiration.”
Edison, an American inventor, created numerous devices that had a profound impact on global life. Known as “The Wizard of Menlo Park” by a journalist, he was one of the pioneers to incorporate mass production principles and large teams into the invention process, which led to the creation of the first industrial research laboratory. With 1,093 U.S. patents to his name, as well as numerous patents in the UK, France, and Germany, Edison is regarded as one of the most prolific inventors of all time. His groundbreaking contributions significantly advanced mass communication, particularly in the field of telecommunications.
15. Nicolas Copernicus 1473 – 1543

“Mathematics is written for mathematicians.”
Copernicus, a Polish astronomer and mathematician, was the first to present a heliocentric model of the universe, shifting Earth from the center of cosmic existence. His groundbreaking book, *De Revolutionibus Orbium Coelestium* (On the Revolutions of the Celestial Spheres), is widely considered the starting point of modern astronomy and the spark that ignited the Scientific Revolution. A true Renaissance man, Copernicus was also a physician, classical scholar, translator, Catholic cleric, jurist, governor, military leader, diplomat, and economist. Despite his many roles, astronomy was his secondary pursuit, yet it was in this field that he left an indelible mark on the world.
14. Alexander Fleming 1881 – 1955

“It is the lone worker who makes the first advance in a subject; the details may be worked out by a team, but the prime idea is due to enterprise, thought, and perception of an individual.”
Fleming, a Scottish biologist and pharmacologist, was a prolific contributor to the fields of bacteriology, immunology, and chemotherapy. He is best known for discovering the enzyme lysozyme in 1922 and the antibiotic penicillin, derived from *Penicillium Notatum* in 1928. For these monumental discoveries, Fleming was awarded the Nobel Prize in Physiology or Medicine in 1945, shared with Howard Florey and Ernst Chain.
11. James Clerk Maxwell 1831 – 1879

“There is nothing more practical than a good theory.”
A Scottish mathematician and physicist, Maxwell's greatest contribution was his formulation of the classical electromagnetic theory, which unified previous isolated findings, experiments, and equations in electricity, magnetism, and optics into a cohesive theory. His famous Maxwell's equations revealed that electricity, magnetism, and even light are all different expressions of the same phenomenon: the electromagnetic field. Following his work, classical laws and equations in these fields were seen as particular cases of Maxwell's broader theory.
Maxwell also contributed to the development of the Maxwell distribution, a statistical model for describing the kinetic theory of gases. These two discoveries played a pivotal role in the emergence of modern physics, setting the stage for advancements in special relativity and quantum mechanics. Additionally, Maxwell is renowned for capturing the first true color photograph in 1861.
Maxwell is often regarded by physicists as the most influential scientist of the nineteenth century for twentieth-century physics. His groundbreaking work is considered by many to be on par with the achievements of Isaac Newton and Albert Einstein. In 1931, on the 100th anniversary of Maxwell's birth, Einstein described Maxwell's contributions as “the most profound and the most fruitful that physics has experienced since the time of Newton.”
For the most influential scientists numbered 1 to 10, see the first list in this series.
This article is licensed under the GFDL because it contains quotations from Wikipedia.
Contributor: Mongoose
12. Louis Pasteur 1822 – 1895

“Fortune favors the prepared mind.”
Louis Pasteur, a French chemist and biologist, is renowned for his groundbreaking work in understanding the causes and prevention of diseases. His research validated the germ theory of disease, significantly reducing deaths from puerperal fever (childbed), and he developed the first rabies vaccine. Pasteur became widely recognized for his invention of pasteurization, a method that prevents milk and wine from causing illness. He is considered one of the founders of microbiology, alongside Ferdinand Cohn and Robert Koch, and also contributed to chemistry with discoveries such as the asymmetry of crystals.
13. Ernest Rutherford 1871 – 1937

“All science is either physics or stamp collecting.”
Rutherford, a physicist and chemist from New Zealand, is celebrated as the father of nuclear physics. His discovery of Rutherford scattering through the gold foil experiment laid the foundation for the atomic orbital theory. In recognition of his groundbreaking work, he was awarded the Nobel Prize in Chemistry in 1908.
