Demetrios Eginitis (1862-1934), one of the most eminent modern Greek astronomers, directed the National Observatory of Athens for 44 years (1890-1933). He was its fourth director since its founding, the one who modernized the Observatory, which was in a state of inactivity after the death of Julius Schmidt in 1884. Eginitis ordered the purchase of adequate instruments, educated the personnel, enriched the library with necessary and up-to-date books and arranged for new buildings to be built in order to install the new telescopes and accommodate the personnel. Moreover, he divided the National Observatory of Athens into three separate Departments: the Astronomical, the Meteorological and the Geodynamic, establishing several meteorological and rain-gauging stations throughout Greece. Major innovations were also introduced by Demetrios Eginitis in the Greek society, beyond the strictly astronomical work. He contributed to the adoption of the Eastern European time zone for the civil time in Greece and he succeeded in changing the official calendar from the Julian to the Gregorian. Having served twice as Minister of Education, he created many schools, founded the Academy of Athens and the Experimental School of the University of Athens. Eginitis was fluent in French, German and English, and therefore was the official representative of his country in numerous international conferences and councils.