Dietrich (Theoderich, Theodoric) of Haldensleben (died 25 August 985) was a count in the Schwabengau, later also in the Nordthüringgau and the Derlingau, who was the first Margrave of the Northern March from 965 until the Great Slav Rising of 983.
He may have been a son of Count Wichmann the Elder and Frederuna, sister of Queen Matilda, and held large estates along the Elbe and Saale rivers.
A henchman of the royal Ottonian dynasty, Dietrich in 953 supported King Otto I of Germany against his revolting son Duke Liudolf of Swabia.
Together with Archbishop Adalbert of Magdeburg he enforced the Christianization of the local Slavic population and was instrumental in the execution of his rival Gero, Count of Alsleben.
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.