Kramers born 1894 Rotterdam to physician father. Studied math physics Leiden got master's 1916. Joined Bohr Copenhagen 1916 did PhD on atomic transitions. Earned PhD Leiden 1919 under Ehrenfest. Worked Bohr's group ten years associate professor Copenhagen. Co-authored failed BKS theory 1924-5. Developed Kramers-Heisenberg dispersion formula 1925 with Heisenberg. Co-authored WKB method 1926. Introduced renormalization quantum field theory 1948 nonrelativistic. Credited Kramers-Kronig relations with Kronig on causality. Known Kramers turnover thermal barrier crossing. Kramers degeneracy theorem named after him. Professor Utrecht 1926 supervised Koopmans. Succeeded Ehrenfest Leiden 1934. Cross appointment Delft 1931-death. Founded Mathematisch Centrum Amsterdam. Married 1920 three daughters one son. Royal Netherlands Academy member 1929 forced resign 1942 rejoined 1945. Won Lorentz Medal 1947 Hughes Medal 1951. Died 1952.