Percival Lankin
Percival Lankin was the author of a pulpy-looking book called The Infinity Rassilons, of which Jenny Nowhere once summoned a worn copy into her hands before handing it to the First Doctor of the 89067986779811167562948736197891674912223184th Universe. Nowhere had just explained the Doctor's place in the Multiverse and the nature of the Batrachian Casket to him; she claimed everything she had just told him was outlined in the book. (PROSE: How To Steal Timeships & To Influence Time Lords)
Behind the scenes
Lankin's The Infinity Rassilons is an obvious reference to The Infinity Doctors by Lance Parkin, a Doctor Who anniversary novel with much to say on Doctor Who continuity and the coexistence of different versions of the Doctor Who universe. "Percival Lankin" would be used again as a stand-in for Lance Parkin in Aristide Twain's Love & War, written as part of the licensed Doctor Who spin-off Dionus.