The California Institute of Technology (CalTech) rose to prominence when Robert A. Millikan was called to Pasadena in 1921 as new university president. Millikan was known for his far-reaching ambitions both as a physicist and as a science manager. He put CalTech on the map as a top university by inviting the world's most renowned scientists for guest lectures and by hiring internationally distinguished scientists to new chairs. With theoretical physicist Paul Epstein, a pupil of Sommerfeld's, Millikan brought modern atomic physics to CalTech in the early 1920s, and with Kármán, he pursued the same strategy a few years later in order to lure the best available aerodynamicist from Europe to Pasadena.