Theodoric IV, Landgrave of Lusatia, also called in German Diezmann, or Dietrich III (c. 1260 – probably 10 December 1307 in Leipzig) was a member of the House of Wettin.
Theodoric was born in 1260, the third son of Margrave Albert II of Meissen and his wife Margaret of Sicily.
After Theodoric and Frederick had come of age, they and their elder brother Henry fought a war against their father, who wanted his son Apitz, from his second marriage with Kunigunde, to inherit the Landgraviate of Thuringia.
In 1301 Archbishop Burchard II of Magdeburg sold Theodoric the castles in Droyßig and Burgwerben for 2000 marks of Stendal silver, with the option to buy them back later.
Theodoric and his brother Frederick armed civilians and peasants and with some assistance from knights from Brunswick they defeated Albert in the Battle of Lucka on 31 May 1307.