Bela of Saint Omer was a French knight, descended from a Fauquembergues family who were castellans of the eponymous castle of Saint-Omer.
[1] His father, Nicholas I of Saint Omer, received lands in Boeotia in the aftermath of the Fourth Crusade.
[2] He later married Margaret of Hungary, the widow of Boniface of Montferrat, Lord of Thessalonica (died 1207).
[4] Bela, who was named after his maternal grandfather, Béla III of Hungary, was the eldest son of the couple, and was followed by his brother William.
[2][4] In 1240, Bela married the sister of the Lord of Athens and Thebes, Guy I de la Roche.