Article: Protestantism is a form of Christian faith and practice which originated with the Protestant Reformation,[a] a movement against what its followers considered to be errors in the Roman Catholic Church. It is one of the three major divisions of Christendom, together with Roman Catholicism and Eastern Orthodoxy. Anglicanism is sometimes considered to be independent from Protestantism.[b] The term derives from the letter of protestation from Lutheran princes in 1529 against an edict condemning the teachings of Martin Luther as heretical.

Question: Who wrote a letter protesting the condemnation of Martin Luther?
Lutheran princes