Pafnuty Chebyshev was a prominent Russian mathematician born on May 16, 1821. He is best known for his contributions to number theory, probability, and approximation theory. Chebyshev developed the Chebyshev inequality, which provides a way to estimate the probability of a random variable deviating from its mean. In addition to his work in probability, Chebyshev made significant advancements in the field of polynomial approximation. He introduced the Chebyshev polynomials, which are used in various applications, including numerical analysis and engineering. Chebyshev's influence extends to many areas of mathematics, making him a key figure in the discipline.