Who are the smartest people on earth? Names like Albert Einstein, Isaac Newton, and Leonardo da Vinci usually top the list, joined by other remarkable thinkers who changed how we understand the world. But defining intelligence is far from simple. Is it measured by IQ, creativity, discovery, or achievement? Some sources suggest an IQ above 140 represents near-genius ability, a level reached by only around 0.4% of people. Still, most historical geniuses never took standardized IQ tests, making their scores estimates.