Sigfried (or Siegfried) was count of the Ardennes and the first person to rule Luxembourg. He was an advocate of the abbeys of St. Maximin in Trier and Saint Willibrord in Echternach. He may have been the son of Count Palatine Wigeric of Lotharingia and Cunigunda. He was the founder of the House of Luxembourg, a branch of the House of Ardennes.
Siegfried held possessions from his father in Upper Lorraine. Although his title of "count" is not disputed, the extent of the lands he possessed remains unclear.
In the mid-10th century, Siegfried acquired the rocky promontory known as Lucilinburhuc and its immediate surrounding area, as well as usage rights for the river from the Abbey of Saint-Maximin in Trier; this was in exchange for land he owned near Feulen. The deed for the exchange was not drawn up until 987; although the plots of land involved were tiny, the transaction was evidently a significant one, for the document bears the seals of Bruno, archbishop of Cologne and brother of emperor Otto I; Henry, archbishop of Trier; and Frederick I, Duke of Upper Lorraine, who was Siegfried's brother.
In 963 Siegfried built a stronghold, a castellum Lucilinburhuc, around which a town started to grow. The structure may have been a refurbishment of an existing building. Siegfried gradually extended his territory towards the west, avoiding the Abbey's lands and those of the emperor.
Though Siegfried used the title of count, the title "count of Luxembourg" was only applied to William I some 150 years later.