Godfrey of Bouillon, who had a sworn allegiance to Henri IV of France, set out on the First Crusade at the urgings of Pope Urban II. Even before he'd embarked upon the mission, rumors were circulating that Godfrey was planning to use the trip to avenge the death of Christ by killing Jews; the Chief Rabbi of Mainz got wind of it and appealed to Henri IV to prevent the knight's journey. Meanwhile, the nearby European Jewish communities that Godfrey proposed to pass through paid off the knight to leave them alone...and so when Henri asked for his guarantee that he would not harm the Jews, the blackmailer appeared to graciously claim that he would let them be.
Godfrey traveled through Hungary on what was purportedly the same route Charlemagne had taken to the East, arriving in Constantinople in December, 1096. The knight was invited to meet its emperor, Alexius Comnenus, who hoped to extract from him an oath of homage -- the Byzantine ruler was not at all happy to let countless rough Europeans traipse through his lands, and hoped by making nice with their leaders he could get them in and out with the least amount of damage. Godfrey refused to take the oath. When Alexius withheld the supplies he had made contingent upon the knight's acceptance, the Crusaders retaliated by raiding the local villages. In April, 1097, Godfrey and his men attacked the palace gate itself, but in the end he and his vassals had to admit defeat and take Alexius's oath to achieve any cooperation from the locals. Even then the Byzantines had to bribe them to be sure they would keep their word to do no further harm to the city.
Now, Tancred, grand-nephew of Roger of Sicily, was part of a large, much-propertied Norman family that joined the Crusade to extend their power and holdings in the East. At Constantinople, Tancred's uncle Bohemond, with whom Tancred was traveling, tried to work the paying-homage-the-the-emperor angle to his own advantage, asking Alexius to create for him the deputy position of Grand Domestic of the East (even though Alexius had no interest in joining the Crusade, and thus no interest in deputizing anyone to do it for him). The emperor was no fool, and agreed to support the Norman army to be sure they wouldn't turn against him as Godfrey and his followers had done.
