Martin Luther started his life out as a firm believer in Christ. He began studing the bible when he was old enough.
Luther, learned while studying the bible that we are saved by faith.
Luther did not like what the church was teaching about faith and good works.
He really didn't like that the church was selling indulgences so you would go to heaven faster.
So what Luther did was he wrote down 95 things that he did not like about the church, called the 95 theses.
Luther kept writing his ideas about God, grace and faith. His writings were printed and spread far and wide. He ever translated the bible into German, so that ordinary people in his country could read it.