The phrase "great reformer" refers to someone who initiates positive and significant changes or improvements in a particular field or aspect of society. Full definition
There are some people placed as party chairman to be great reformers of the party. (conservativehome.blogs.com)
Martin Luther, for example, that great reformer who battled the Catholic church over the issue of how to receive eternal life, called the book of James, «a right strawy epistle» meaning that there was nothing in it but wood, hay and stubble. (redeeminggod.com)
Why didn't 12th - century corruption give rise to atheism rather than giving rise to great reformers like St Francis of Assisi? (faith.org.uk)