If you're writing an essay on this topic, you could defend either viewpoint.
Martin Luther was critical in the creation of the Protestant Reformation. Other reformers who preceded him (such as Wycliffe in England and Hus in Bohemia) had focused more on abuses and errors within the Roman Catholic system, such as money-grabbing practices of the church, clergy corruption, papal supremacy, offering of only one element (bread) in the sacrament, etc. Luther addressed such symptoms of the problem too, but was more targeted than his predecessors in targeting the central tenets of Roman Catholic doctrine as the primary problem that needed to be changed. Luther attacked the theology of the "scholastics" (the university teachers of theology) who advocated "doing what is in you" to gain favor with God, and Luther fought their philosophy with his emphasis on salvation coming solely by grace from God.
At the same time, Luther was very much the right man at the right time. His training in the church equipped him to stand toe-to-toe with other scholars and leaders of the established church. The papacy's power to silence its opponents was weaker in Luther's time than it had been a century earlier when Hus was executed. Political events also helped Luther, as an election (by seven appointed princely electors) was taking shape at the same time as Luther's protest began. Since Luther's prince, Frederick of Saxony, was one of those electors and the pope was seeking to influence Frederick's vote, Luther's prince was in a strong position to protect his subject from Rome taking immediate action against him.
