Specifically, was he the catalyst? Why did he deny the peasants? Theology? Political maneuvering?
A reply to /u/Kugelfang52
This is a very good question. Most of the scholarship I am aware of say that the Peasants' Revolt and the greater Protestant Reformation share the same causative factors, but that they arose with a high degree of independence between them.
More specifically, there were a few factors to consider if we are to talk of German-speaking lands in the 1520s.
Changing social order. We already saw the lesser Knights rise up in revolt in 1522-23 in the so-called Knights' Rebellion in the Rhineland where lesser Knights attempted to reverse the new order dominated by burghers and a new style of warfare centered around the Landsknechts. The result was a combination of declining value of rural agriculture and declining prestige of knights as warfare shifted to large units of armed infantry. The leader Franz Sickingen had also supported Lutherans and helped print Lutheran propaganda. So as their movement turned to armed rebellion, Luther viewed this as liability, fomenting an argument among his supporters as to who had authority in Germany. In this period, Luther wanted to gain the support of Princes, however he saw them as favoring the status quo. This is around the time that Luther and Melanchthon espoused the idea of "Two Kingdoms", that the church should not exercise worldly government, and that temporal princes of the church could not also be saviors of souls. Further, the temporal world needed laws, endowed by God, through which it should be governed. However, as most people could not clearly know the boundary, they should submit to the authority of princes.
Socio-economic enmity between landlords and tenant farmers (Bauern in German). The second half of the 1400s had seen labor shortages in Germany due to various factors. This allowed tenant farmers (translated to "peasants") to negotiate better conditions for work and living. In southwestern Germany, most of the landlords were minor princes both ecclesiastical and secular, under the Holy Roman Empire. Now the landlords attempted to push their tenant farmers into serfdom.
These tenant farmers and their leaders had been exposed to the ideas of Luther, Melanchthon, and Zwingli. They saw their landlords -- largely wealthy monasteries, bishops and archbishops -- as exceeding their authority and abusing their office. Pointedly, they saw these landlords as abusing the true law which should favor the well being of the tenant farmers, or at least not be abused to push them into serfdom. Zwingli had preached that the Scripture should provide the law, thus providing a strong rationale in the Peasants' movement. The preacher Thomas Muntzer was a key leader in fomenting the rebellion, preaching from church pulpits, stating that to be held as a serf is to go against the Scripture. Thus, Muntzer promulgated a religious justification for the rebellion.
In 1525 the leaders of the rebellion printed the so-called "Twelve Articles" which distanced them from many of Muntzer's ideas, in particular it did not mention Muntzer's visions of the pending apocalypse. Instead, the Twelve Articles focused on socio-economic-political reforms such as abolotion of serfdom, rationalization of tithes (there were several!) and how they are to be used, restoration of pastures and forests, further privileges on labor, taxes, rent, and of course a reform of the justice system. Addressing this, Luther wrote that he supported their plight but that he rejects their violent means, and the Scripture did not justify this.
Luther himself was initially sympathetic to the plight of the peasants, but as the rebellion rose in violence he wrote two strong responses: An admonition to peace, and a few weeks later Against the robbing and murdering hordes of peasants. In the first, he wrote that the duty of humans in this world was to work, and therefore the duty of the farmers was to labor in the farm. In the second, he portrayed the rebellion as a radical movement run by fanatics, outside the true spirit of his Reformation. Lutherans on the side of Luther began to paint Muntzer as a heretic stirring up violence and bloodshed. They focused on Muntzer's call for a "Christian League" (read: a religious state against the then-present HRE), iconoclasm, refusal to pay tithes, adult baptism, and apocalyptic visions.
So in reviewing this topic, it is important to view the evolution of Luther's own thinking as regards to authority. Political consideration was certainly a factor, as in this period, Luther wanted a moderate Reform whereby the Princes would be the agents of change, as it was both their Godly privilege to be in their station and their Godly duty to correct what he saw as eggregious errors in the Church of the time.
Further reading: