John III Margrave of Brandenburg-Salzwedel nicknamed John from Prague (1244 in Prague – 1268) was the eldest son of Margrave Otto III and his wife Beatrice of Bohemia.After his father died in 1267 he ruled the Margraviate of Brandenburg jointly with his brother Otto V and his cousins Otto IV and Henry I.John died during a tournament in 1268. He was unmarried and childless.