Ronald A. Fisher was a British statistician and geneticist who is considered one of the founders of modern statistics and experimental design. He introduced the concepts of variance, likelihood, maximum likelihood estimation, analysis of variance, and the Fisher information.
Karl Pearson was a British mathematician and biometrician who is regarded as one of the pioneers of mathematical statistics and the founder of the eponymous Pearson correlation coefficient, Pearson's chi-squared test, and the Pearson distribution.
William Sealy Gosset was an English statistician and chemist who worked for the Guinness brewery and published under the pseudonym Student. He is best known for developing the Student's t-test, t-distribution, and t-statistic, which are widely used in small-sample inference.
Andrey Kolmogorov was a Soviet mathematician who is recognized as one of the greatest of the 20th century. He made fundamental contributions to various fields of mathematics, including probability theory, mathematical logic, functional analysis, and topology. He is also the founder of the Kolmogorov complexity theory and the Kolmogorov-Smirnov test.
Jerzy Neyman was a Polish-American mathematician and statistician who is one of the co-creators of the Neyman-Pearson lemma and the Neyman-Pearson criterion for hypothesis testing. He also developed the theory of confidence intervals, the Neyman-Rubin causal model, and the Neyman-Scott cluster process.