Peter the Hermit
In 1095 Pope Urban II, in response to a plea for help from the Byzantine Emperor Alexius I, called on all Christians to travel to the Holy Land and free it from the Muslims. His call for what became known as the Crusade was wildly successful, partly because it was spread widely by itinerant preachers. Peter, a priest of Amiens, was one such preacher who gathered a huge following. With a red cross sewn to their clothes to mark them as pilgrims, thousands of common people left their lives in Europe and followed him east.
With little food and almost no money, this horde of peasants was forced to live off the land as they passed, and caused enormous damage to the countryside as they passed. In Hungary, the Peasant's Crusade earned the enmity of King Coloman by sacking the town of Semlin, and when they crossed into the Byzantine Empire they fired the city of Belgrade. Under the orders of Alexius I, Byzantine troops attacked the peasant army, but the survivors were allowed to approach (but not enter) Constantinople.
Peter the Hermit successfully negotiated passage across the Bosphorus, where his "army" met with a smaller, more professional force under Walter the Penniless. Rather than wait for the armies which were making their way east, Peter and Walter marched blindly inland and attacked the Turks. While Walter invested the castle of Xerigordon, Peter's mostly French force, striking from the Byzantine garrison of Civetot, ravaged the lands around Nicaea, which they lacked the engines to besiege. After returning to Civetot and selling their plunder to the Byzantines, Peter led his men back into Turkish territory.
Only a few miles from camp, Peter's poorly-armed and undisciplined force were ambushed by Turkish soldiers and slaughtered. A handful of survivors, including Peter himself, managed to escape to Civetot and eventually made their way back to Constantinople, where they waited for the rest of the Crusaders.
Peter the Hermit resumed the crusade in the councils of the lords, but was of little importance. Except for a notable speech boosting morale at the siege of Antioch, he is little-mentioned in the histories afterwards. It appears that, after the fall of Jerusalem, he returned to France and founded a church of the Holy Sepulchre, where he served as prior until his death in 1131.