Lionel Correll was an American investor.
He told the Eighth Doctor about the auction at Gordon and Painswick of Fitz's 1893-94 journal. He helped the Doctor drive up the price to find out who was interested in purchasing it. (PROSE: Time Zero)
The Doctor met Correll again when he was investigating the crystals being left behind by agents of the Council of Eight. He informed the Doctor that Ernest Fleetward was conducting research into similar crystals. (PROSE: Sometime Never...)