Joscelin of Louvain, also spelled Jocelin de Louvain and Jocelyn of Leuven, was a nobleman from the Duchy of Brabant who settled in England after his half-sister Adeliza of Louvain married King Henry I. There Joscelin married an English heiress, and through his son, the House of Percy—as the Earls and later the Dukes of Northumberland—became the most powerful family in Northern England. Wikipedia