Poppo von Osterna (died 1257) was the ninth Grand Master of the Teutonic Knights, serving from 1252-56 or 1257.Poppo hailed from a family with rich knightly traditions which resided in Osternohe, just outside Nuremberg in Franconia. He joined the Teutonic Order in 1228 and was one of the first friars to settle in Prussia. In 1233, Poppo took part in localisation of the town of Kulm (Chełmno). He became the Prussian Master in 1240 and in 1241 fought in the Battle of Legnica although the participation of the Teutonic Knights in the battle is questionable. In 1242 Poppo went to Austria with a German legation to collect money for war with Duke Świętopełk II of Pomerania. From 1248-53, Poppo resided in Germany, becoming the ninth Grand Master in 1253. The pro-papal minority did not agree with the capitulum's choice and chose Wilhelm von Urenbach as their rival Grand Master.After being chosen Grand Master, Poppo went to Prussia to start a war against the Sudovians.In 1254 he went with a legation to King Ottokar II of Bohemia and received needed military help to start crusades in Sambia in 1254 and 1255. After the conquest of Sambia, Poppo built several castles around the Vistula Lagoon, including Königsberg.While Landmeister, Poppo supposedly led a detachment of Teutonic Knights at the Battle of Legnica in 1241 and was killed by the Mongols. However, the presence of Teutonic Knights in the battle is uncertain. Poppo did die and was buried at Legnica (Liegnitz), but years later while visiting his wife's nunnery and after serving as Grand Master.