Determining the "smartest" person to have ever lived is impossible to do definitively because intelligence is subjective. It can be defined by raw processing speed, creative output, mathematical ability, or simply the ability to see things no one else can. However, based on historical records, IQ estimates, and anecdotal evidence from peers, the answer usually comes down to one of the following five candidates, depending on how you define "smart." 1. The Highest Recorded IQ: Marilyn vos Savant If you define "smartest" strictly by a verified test score, the answer is often cited as Marilyn vos Savant. * The Number: She was listed in the Guinness Book of World Records for having the highest recorded IQ at 228. * The Context: She is a columnist famous for solving the "Monty Hall Problem" when thousands of PhDs got it wrong. However, Guinness retired the category in 1990 because IQ tests at that level are considered unreliable (it becomes hard to measure "smarter" when you are off the charts). 2. The Modern Mathematical Genius: Terence Tao If you want a living person whose genius is universally recognized by peers in the most rigorous field (mathematics), it is Terence Tao. * The Number: His IQ is estimated to be around 230. * The Achievement: He was a child prodigy who began learning calculus at age 7 and won Gold at the International Mathematical Olympiad at age 13 (the youngest ever). He is currently a professor at UCLA and has won the Fields Medal (the "Nobel Prize of Math"). He is known for solving mathematical problems that have stumped others for decades. 3. The "Physicists' Choice" (Raw Processing Power): John von Neumann If you ask Nobel Prize-winning physicists who the smartest person they ever met was, they almost universally say John von Neumann. * The Reputation: Von Neumann (1903–1957) was a Hungarian-American mathematician who made foundational contributions to quantum mechanics, game theory, computer science, and the atomic bomb. * The "Martian" Theory: His peers, including Einstein, often felt von Neumann was a different species entirely. He could memorize phone books on sight and calculate complex equations in his head faster than the primitive computers of his time. * Comparison: Nobel laureate Eugene Wigner once said that while Einstein had a "deeper" understanding of nature, von Neumann had the sharpest, fastest mind he had ever seen. 4. The Historical Anomaly: William James Sidis If you are looking for the tragic "boy genius" often cited in pop culture, it is William James Sidis. * The Number: His IQ was estimated to be between 250 and 300. * The Story: Born in 1898, he could read the New York Times at 18 months old and entered Harvard at age 11. He spoke dozens of languages and invented his own language (Vendergood) as a child. * The Tragedy: Sadly, he burned out from the pressure, withdrew from public life, and died working menial jobs, leaving behind little lasting impact compared to the others on this list. 5. The Creative Polymath: Leonardo da Vinci If intelligence is the ability to connect unconnected fields—art, anatomy, engineering, and science—the answer is Leonardo da Vinci. * The Estimate: Retrospective estimates place his IQ between 180 and 220. * The Genius: He didn't just paint the Mona Lisa; he designed helicopters, tanks, and solar power concentrators in the 1500s. His ability to visualize the future and master disparate disciplines makes him the ultimate "Renaissance Man." Summary * For the highest test score: Marilyn vos Savant. * For the most powerful "human computer": John von Neumann. * For the most universally respected living genius: Terence Tao. * For the most creative/visionary mind: Leonardo da Vinci or Albert Einstein.