The best answer for this is to say that Martin Luther was the person who started the Reformation. Luther did not start the Reformation by himself. There were other people, like John Calvin, who were important in it, but Luther is the person most usually seen as the initiator of the movement.
Martin Luther was the man who really got the Reformation started. Other people had had ideas about reforming the Catholic Church, but it was Luther who took the step that actually led to the Reformation. He did this in 1517 when he put forth a series of statements (his "95 Theses") about what was wrong with the Church. From there, he kept pursuing the idea that the Church needed to change. This was the start of the Reformation.
A German Monk, named Martin Luther is credited with starting the Protestant Reformation. Martin Luther realized that the Catholic church was corrupt and there were many issues that needed to be addressed such as the selling of "indulgences". Luther posted his 95 thesis on the church door and annoucned the corruption that he saw in the church. Luther believed that the church was not the final religious authority, but that scripture should be looked to as the final authority for believers. Eventually his actions resulted in a break with the Catholic church and his followers become known as Lutherans. Luther also believed the people were saved by grace through faith in the word of God, and not by going along with everything that the Catholic church proclaimed to be true.