Aleksander Gieysztor was a Polish medievalist historian. He was born in Moscow to a Polish family. He lived in Warsaw since the age of five. He graduated in history from Warsaw University in 1937. He was married to Irena Gieysztorowa, a fellow historian. The Aleksander Gieysztor Prize of the Kronenberg Foundation and the Aleksander Gieysztor Academy of Humanities are named after him.