In 1614, the evil Vincent Fettmilch organized an attack on the Jewish quarter of Frankfurt, and the Jews were subsequently expelled from the city. Thanks to the Emperor’s intervention, two years later the Jews were allowed to return to the city in honor, and Vincent and his cohorts were hanged. The Jewish community marked the date of 20 Adar as a yearly day of celebration, naming it “Purim Vincent.” (Yosef Ometz §1109)
Link: Purim Vincent
R. Shlomo Zalman Auerbach was a renowned halachic authority who lived in Jerusalem. Many of his rulings pertain to modern technological advances as they apply to Jewish life.
Link: Contemporary Halachah
Adar 20 is the yahrtzeit (anniversary of the passing) of Rabbi Yoel Sirkes (1560?-1640), Rabbi of Krakow and author of the Bayit Chadash ("Bach") commentary on the great Halachic work, the Arba'ah Turim.