Robert III, the Bellicose (German: Ruprecht der Streitbare; died 1191), was co-Count of Nassau between 1160 and 1191. The House of Nassau would become an important aristocratic family in Germany, from which are descended the present-day Kings of the Netherlands and Grand Dukes of Luxembourg.
Robert was the younger son of Count Arnold I of Laurenburg from the House of Nassau and Anastasia, daughter of Count Ludwig II of Arnstein an der Lahn. His father was Count of Laurenburg and the younger brother of Robert (Ruprecht) I.
From 1160, Robert III was Count of Nassau and ruled the possessions of Nassau together with his brother Henry (Heinrich) I and his cousin Walram I, son of Robert I. He became the Münzherr of Siegen in 1170, the Vogt of Schönau Abbey in 1172, and Vogt of Koblenz in 1182. Robert III was a loyal supporter of the Hohenstaufen Emperor Frederick I Barbarossa and escorted him in the Battle of Monte Porzio in 1167 and the Battle of Legnano the 1176. He also participated in the Empire’s wars against Henry the Lion in 1180-1181.
With his cousin Walram I, Robert joined the Third Crusade (1189–1190), acting as the imperial standard-bearer in Frederick’s army. Walram and Robert were part of Frederick I’s delegation set ahead to Constantinople to prepare for the arrival of the German troops. While Frederick had earlier received promises of cooperation from Byzantine Emperor Isaac II Angelos, the delegation was initially snubbed and then actually held as hostages by the Emperor. Robert died on the way back from the Crusade while yet in the Holy Land in 1191.