Pafnuty Chebyshev

Pafnuty Chebyshev was a Russian mathematician who made foundational contributions to probability theory, statistics and number theory. He proved a general form of what is now called Chebyshev's inequality, which places a bound on how much of the probability distribution of a random variable can lie far from its average value, a result that holds true for a very wide range of probability distributions and became a fundamental tool of probability theory and statistics. In number theory, Chebyshev's work on the distribution of prime numbers produced some of the strongest results obtained before the prime number theorem was finally proved decades later, including a proof of Bertrand's postulate, which states that for any integer greater than one there is always at least one prime number between it and its double. Chebyshev founded an influential school of mathematics at Saint Petersburg University, sometimes called the Saint Petersburg mathematical school, which trained a number of important later Russian mathematicians, and the class of orthogonal polynomials that bear his name, Chebyshev polynomials, developed in connection with his work on approximation theory, remain widely used tools in numerical analysis and engineering.