Caspar René Gregory published a cataloging system for the Greek New Testament manuscripts in 1908. In 1963, Kurt Aland expanded Gregory's work, and the Gregory-Aland (GA) numbers became the industry standard for referencing Greek New Testament manuscripts.
Gregory was born in Philadelphia. After completing his bachelor's degree at the University of Pennsylvania in 1864, he studied theology at two Presbyterian seminaries: in 1865–1867 at the Reformed Presbyterian Theological Seminary, Philadelphia, and in 1867–1873 at the Princeton Theological Seminary. In 1873, he decided to continue his studies at the University of Leipzig under Constantin von Tischendorf.