Haclav Agusti Prydonius was a hero of ancient Gallifrey. He and the crew of his ship, the Apollaten, went on a quest to Thule to overthrow the reign of a marauding Sphinx. He returned home with the Sphinx's head, which was donated to the Academia Library for study. At first, Prydonius rejected Rassilon and his Neo-Technologist views but later became his supporter, as the Admiralty was angry at the lack of funding for the Empire Fleets. After Prydonius publicly denounced the Pythia, the Court of Principals made him a noble and sent him to Funderell in the asteroid archipelago to observe a minor dispute between Ruta III and the Sontara Warburg. (PROSE: Cat's Cradle: Time's Crucible)

The Auton Doctor quoted Prydonius when the Tremas Master told him that the vortex driller that they were on was said to be made from the stones of the first Prydonian Chapterhouse, saying "If they lay foundations out in infinity, let them be ours." (AUDIO: The Auton Infinity)