Martin Luther — the original Martin Luther (1483-1546) — was, of course, the founder of the Protestant Church. The Baptist sect, one of its branches, was the denomination of King Sr. and Jr. — one of whom succeeded the other as pastor of Atlanta's Ebenezer Baptist Church.
Luther was a rebel. "Here I stand, I can do no other," he famously said.
The very name — Protestant — has "protest" built into it. His church valued individual conscience, standing up to oppressive authority — which, in the 16th century, was the Catholic Church.
In MLK's day, the oppressive structure was racism. And he fought it with marches, speeches, sit-ins. He was arrested, his followers were beaten. But he refused to budge. "Here I stand."
A fateful trip
It's likely that King Sr. — "Daddy King" — was made newly aware of the history of Martin Luther, and his resolute personality, during a 1934 pilgrimage to Germany, the land of Luther's birth. It was a momentous trip. A game changer.
That was the year he and his son were rechristened — unofficially, in the case of the boy — "Martin Luther."