Stephen was born into the so-called Ders branch of the gens (clan) Bő, which originated from Somogy County, and was one of the ancient ethnic Hungarian kindreds which had participated in the Hungarian conquest of the Carpathian Basin in late 9th century.
[1] Although Stephen originated from a relatively less significant branch of the Bő clan, his sister married Gregory II Monoszló, a prominent landowner in Southern Transdanubia and Slavonia.
The marriage resulted the rapid political and social grow of Stephen's two sons Michael and Peter "the Toothed" by the end of the 14th century, as their cousins were the influential barons Egidius, Gregory III and prelate Peter Monoszló.
[5] Szűcs also argued Stephen was one of the four noble judges (Hungarian: szolgabíró) in Somogy County since the early 1260s.
[6] Following King Béla IV and his son Duke Stephen together confirmed the liberties of the "royal servants", from then on known as noblemen in their Decree of 1267, the ispán (head) of Somogy County, Lawrence was commissioned to review the ownership of several possessions in the county, as one of the articles of the Decree of 1267 ordained that "the lands of the nobles, which thou art ours, the peoples of the queen's free villages, or the courtiers, or the castle folks, are occupied or kept occupied under any pretext, must be returned to these nobles".