Dmitry Mendeleev was a Russian chemist best known for creating the Periodic Table of Elements. Born on February 8, 1834, he organized elements based on their atomic mass and properties, which helped predict the existence of undiscovered elements. His work laid the foundation for modern chemistry. Mendeleev's first version of the periodic table was published in 1869. He arranged elements in rows and columns, grouping those with similar properties. This innovative approach allowed scientists to understand the relationships between elements better and has been crucial in the study of chemistry ever since.