Siegfried I the Older (Siegfried der Ältere von Walbeck) (d. 15 March 990), Count of Walbeck and Möckerngau, son of Lothar II the Old, Count of Walbeck, and Mathilde von Arneburg. He succeeded his father as Count of Walbeck upon his death.
Siegfried is first mentioned as an ally of Odo I, Margrave of the Saxon Ostmark, in his conflict with Mieszko I, Duke of Poland. In particular, Siegfried fought in the Battle of Cedynia (Zehden), as reported in the Chronicon of Siegfried’s son Thietmar of Merseburg. Both Siegfried and Odo escaped the ensuing slaughter. As an interesting sidebar, Mieszko married Oda of Haldensleben, daughter of Dietrich, Margrave of the Nordmark, who was the predecessor of Siegfried’s brother Lothar I as margrave.
In 979, he and his brothers were appointed regents of the County of Möckerngau by Emperor Otto II. Siegfried consolidated his position as sole count in 983. Later that year, he fought with the Saxon army against the Great Slav Rising revolt against the empire.
In 990, he supported the Empress Theophanu in her war against Boleslaus II, Duke of Bohemia. He then moved against the rebellious Lutici who were threatening Brandenburg. He fell from his horse on 15 March 990 and died.
Siegfried married Kunigunde von Stade daughter of Henry I the Bald, Count of Stade. Siegfried and Kunigunde had five sons:
Upon his death, Siegfried was succeeded as Count of Walbeck by his son Henry.