The Final Chapter was a secret society that once existed within the ranks of the Time Lords.
It was originally a conspiracy between Uriel and Luther who both wished to revolt as well as take over Gallifrey. With their rule, they sought to turn their world into a military power that overturned Rassilon's principle of non-interference. Thus, they created an army of clones that were grown from Uriel's biodata which would be used to take control of the Gallifreyan home world. However, when Uriel saw his "first child"; Xanti, his military ambitions faded and he spirited his son into the Chapterhouse whereupon he fled to the Quantum of Solace to hide from his guilty.
Despite the end of the Final Chapter, Overseer Luther later used clones of Xanti to form a new secret society called the Elysians with the aim of attaining godhood by rewriting his peoples history where he would become all powerful. The secrets of the Final Chapter were later uncovered by the Eighth Doctor who managed to learn this information from Uriel's mind after which he managed to thwart Luther in his plan. (COMIC: The Final Chapter)