Martin Luther was a key figure in the Reformation.
Beliefs
He developed a test for canonicity, asking whether a particular book taught Christ, leading him to question the canonicity of Esther as it is too aggressively Jewish and without gospel content.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher. Pages 76; The ESV Study BibleTM, English Standard Version (ESV) by Crossway Bibles, 2007. Page 849)
Quotations
"Bene orasse est bene studuisse," or "to have prayed well is to have studied well." (Spurgeon's Sermons on Prayer by Charles H. Spurgeon (2007))
List
Martin Luther