Dietrich (or Theodoric, also Theoderic[h]) of Haldensleben (died 25 August 985) was the first margrave of the Northern March from 965 until his deposition in 983. He also bore the title of a Dux (Duke) in contemporary sources.
Probably a member of the House of Billung, the Saxon count Dietrich of Haldensleben in the Nordthüringgau may have been a son of Count Wichmann the Elder with Frederuna, sister of Queen Matilda of Ringelheim. A henchman of the royal Ottonian dynasty, Dietrich in 953 supported King Otto I of Germany against his revolting son Duke Liudolf of Swabia. He also fought - without success - against the Polabian Slavs settling on the Elbe river at the eastern rim of his Eastphalian home territory. In return Emperor Otto appointed him Margrave of the Northern March, the largest part of the former Marca Geronis after its dissolution upon the death of Margrave Gero in 965.
Dietrich was a harsh overlord. Together with Archbishop Adalbert of Magdeburg he enforced the Christianization of the Slavic population and plot the downfall of rivaling Count Gero of Alselben. Owing to his pride as stated by the chronicler Thietmar of Merseburg (he allegedly once refused the marriage of one of his kinswoman to a Slav "dog"), in 983 the Slavic Lutici and Hevelli tribes sacked the lands of the eastern bishoprics of Havelberg and Brandenburg and reverted to paganism. According to Adam of Bremen and Annalista Saxo, Dietrich was deprived of his march in the same year, though he later again appeared as a Saxon general.
He had the following children:
According to the Annals of Quedlinburg Dietrich died on August 25, 985.