The vast majority of what is known about the Slavnik family, is from the works by John Canaparius, Bruno of Querfurt, and Cosmas of Prague. Prince (dux) Slavník (†981), is generally considered as the founder of the dynasty, as there is no other known older relevant personality. He therefore also gave the name to the whole family. According to Bruno of Querfurt, Slavník was the grandson of the Saxon duke Henry I, by maternal line most probably of an unknown Slavic woman, with whom Otto I had an illegitimate son William. This connection explains the friendly relationship between Slavnik's son Vojtěch, Saint Adalbert of Prague, with Otto III, and the Otto's efforts (Congress of Gniezno) around St. Adalbert's canonization, and the installation of Adalbert's brother Radim Gaudentius as the first archbishop of Gniezno Cathedral.