Theodoric I (German: Dietrich von Landsberg; c. 1130 – 9 February 1185), a member of the House of Wettin, was Margrave of Lusatia from 1156 until his death.

[2] When his father retired in 1156 and was succeeded by his eldest son Otto II in Meissen, Theoderic received the Lusatian march (Orientalis marchio) formerly held by Henry of Groitzsch, including the castles of Eilenburg and Landsberg, from the hands of the Hohenstaufen emperor Frederick Barbarossa.

He married Dobroniega, daughter of the Polish Duke Bolesław III Wrymouth and his second wife Salomea of Berg.

[2] An illegitimate son Theodoric, by a mistress named Cunigunde, widowed Countess of Plötzkau, was legitimated on 12 May 1203 and became Bishop of Merseburg in 1204.

In the conflict with Henry the Lion, he actively fought the Saxon duke together with Archbishop Wichmann of Magdeburg and his brothers Margrave Otto II and Dedi of Groitzsch.