Christians worldwide are celebrating the 500th anniversary Tuesday of the Protestant Reformation. Martin Luther, in posting his 95 Theses on the door of a church in Wittenberg, Germany, challenged the church hierarchy of his day, calling Christians back to the Bible and to salvation through faith alone. Luther was fiery, bold and prophetic. And it’s no coincidence that he’s the namesake of the most significant religious figure in U.S. history: the Rev. Martin Luther King Jr. Few people know the story of the connection between the two reformers.

What they share in common is far greater than a name. The story begins in 1934, when King’s father traveled to Berlin to attend the Fifth Baptist World Alliance Congress. There, he and 29 other black ministers helped racially integrate the Congress in the face of a “color ban.” They also condemned the rising anti-Semitism they saw in Nazi Germany. While in Berlin, Michael King Sr. (as he was then known) learned about Luther’s denunciations against the injustices of the medieval penitential system. Luther’s struggle resonated with King, who wondered what such boldness might mean for racial injustice in the United States. Luther’s legacy left such an impression on King that he changed his name, and the name of his then-5-year-old son, to Martin Luther King. Although King Sr. would go on to make his own courageous stand for social justice, his son’s life and legacy was destined to more closely mirror that of the monk from Germany.

Both Luther and King Jr. publicly protested the exploitation of the poor. Luther’s objections to the Catholic Church’s teachings on justification (how people are saved) came to a head over indulgences. At the time, indulgences could be purchased to grant remission of penalties for sins. Indulgences became a means of widespread economic exploitation, preying on the poor’s fear of punishment in the afterlife. On All Saints Eve of 1517, Luther nailed his 95 Theses to the Wittenberg church door to denounce the sale of indulgences and invite church leaders to a public debate. This was a calculated public protest. It was meant to dramatize the suffering of the marginalized in a way that the powerful could not ignore.

Luther’s 43rd thesis states, “Christians are to be taught that he who gives to the poor or lends to the needy does a better deed than he who buys indulgences.” Even more provocative was Luther’s 45th thesis: “Christians should be taught, he who sees his neighbor in distress and, nevertheless, buys indulgence is not partaking in the Pope’s pardons, but in the wrath of God.” Luther protested both doctrinal errors and the social exploitation that they led to. Luther’s heirs are known as Protestants today because his movement was so centered on protest.

Nearly 450 years later, King would likewise use public protest to confront the social devastation of false doctrine.