Johannes Brønsted was a Danish chemist born on February 22, 1879, and he is best known for his contributions to acid-base theory. In 1923, he proposed the Brønsted-Lowry theory, which defines acids as proton donors and bases as proton acceptors. This theory expanded the understanding of acid-base reactions beyond the limitations of the earlier Arrhenius theory. Brønsted's work laid the foundation for modern physical chemistry and has had a lasting impact on various fields, including biochemistry and environmental science. He also contributed to the study of catalysis and reaction mechanisms, further enhancing the understanding of chemical processes.