Short answers, pulled from the story.
The Codex Gregorianus was compiled by a man named Gregorius, about whom almost nothing is known for certain. Scholars have suggested he served as the magister libellorum, drafter of responses to petitions, under emperors Carinus and Diocletian in the 280s and early 290s.
The Codex Gregorianus is believed to have been produced around 291-294 AD, though the exact date is unknown. It collected imperial constitutions spanning from the 130s to the 290s AD.
The Codex Gregorianus contained rescripts to private petitioners, letters to officials, and public edicts issued by Roman emperors over roughly a century and a half. The material was organized into thematic headings called tituli and arranged chronologically within each heading. Scholars estimate the work ran to 15 books, with estimates ranging from 14 to 16.
The directive ordering the compilation of the Codex Theodosianus, addressed to the senate of Constantinople on the 26th of March 429 and drafted by Theodosius II's quaestor Antiochus Chuzon, explicitly cited the Gregorian and Hermogenian Codes as the model for organizing imperial constitutions since Constantine I.
The Codex Gregorianus was superseded by two sixth-century codifications. The Breviary of Alaric, promulgated in 506, explicitly replaced the full text throughout Visigothic Gaul and Spain. Justinian's Codex Justinianeus, which came into force in 529, incorporated and displaced it across the eastern empire, North Africa, and Italy.
On the 26th of January 2010, Simon Corcoran and Benet Salway at University College London announced the discovery of seventeen fragments believed to be from the original version of the Codex Gregorianus.