Leonida Tonelli was an Italian mathematician born on March 17, 1885, in Pisa, Italy. He is best known for his contributions to the field of mathematical analysis and functional analysis. Tonelli developed the Tonelli theorem, which is significant in the study of integration and measure theory. In addition to his work in analysis, Tonelli made important contributions to calculus of variations and partial differential equations. His research has had a lasting impact on mathematics, influencing both theoretical studies and practical applications in various scientific fields. Tonelli passed away on December 24, 1946.