Pope Urban was the pope who called for the First Crusade. While he made it seem like a noble venture, most historians today think that it was a power play. He say some worth in calling the for a crusade and as a result of his speech and his promises many took up the call.
Alexios I Komnemos was the Byzantine emperor during the time of the First Crusade. His empire was losing lands to the Seljuk Turks. Alexios turned to the West and the Pope for help. This was the launching pad for the First Crusade.
Peter the Hermit was the charismatic preacher who led the People's Crusade. Before the official crusading knights went to war a group of common people took arms and attempted to travel to the Holy Land. Peter led one of the groups but was stopped by the Seljuk Turks. While many in his group were massacred he survived.
Raymond IV of Toulouse was one of the leaders of the First Crusade. His most important battle was the siege of Antioch in October of 1097. It was not an easy battle and took until June of 1098 to win Antioch. He also swore an oath of friendship to Alexious. He was also offered to rule of Jerusalem, but he refused because he did not want to be king of the place where Jesus suffered.
Godfrey of Bouillon was a Frankish crusade leader. One of the many leaders he played a minor, but very important role in key battles. In Jerusalem he and his men built wooden ladders and climbed over the wall. When Raymond refused to be king of Jerusalem, Godfrey took control, but only as a secular leader and not as a king.