Siegfried I (c. 1010 – 7 February 1065) is considered the progenitor of the Carinthian ducal House of Sponheim (Spanheimer) and all of its lateral branches, including the Counts of Lebenau and the Counts of Ortenburg. He is documented as Count of Sponheim from 1044 and served as margrave of the Hungarian March in 1045/46 and as count in the Puster Valley and the Lavant Valley from 1048 until his death.