Who initiated the challenge against the Catholic Church in November 1517, sparking the movement later called the Reformation?

Explanation

Martin Luther is credited with starting the Reformation by posting his Ninety-Five Theses in November 1517, which questioned the practices of the Catholic Church and ignited widespread religious reform. Anne Boleyn and Ulrich Zwingli were important figures later, while Pope Leo X was the pope during this period but not the initiator of the movement.