Count Siegfried I of Luxembourg was a nobleman who lived in the late 10th century. He is best known for founding the County of Luxembourg around 963 AD. Siegfried built the Luxembourg Castle, which became a significant stronghold and symbol of power in the region. Siegfried's lineage played a crucial role in the history of Luxembourg and Europe. His descendants, the House of Luxembourg, would later produce several Holy Roman Emperors and influential rulers. Siegfried's legacy is still recognized today, as he is considered the founder of the Grand Duchy of Luxembourg.