A foolish mortal, driven by his thirst for knowledge, signs away his body and soul. Percival's folly, some might call it.
Percival was born to the von Gikkingen family, a well-known, highly-esteemed, and very rich family from Baldur's Gate. He was held to high standards, praised for his gift of intelligence, and coddled for many years. Percival was picked on throughout his childhood for never really fitting in, though, and it's been internalized ever since, causing his constant attempts to regain the praise he used to get constantly.
Percival has an unending thirst for knowledge, and eventually not even the books at Sorcerer's Sundaries could feed him. He has an incredible collection in his home and surrounded himself, day and night, and could rival most professors with his knowledge, but it wasn't enough for him. He stumbled across a tome that spoke to him, promising the knowledge he seeked for the simple price of handing his body over once he died. Percival agreed, becoming a warlock of Moander.
His feeble mind was flooded with knowledge no mortal should know, and he can't remember half of it without a splitting headaacge. Percival travels now, trying to regain most of the knowledge he lost, writing down everything he possibly can into that tome of his. Safe to say, Baldur's Gate doesn't miss the annoying prick.
Percival was pulled into the ship on accident, but he was thrilled to be thrust directly into danger, seeing it as another opportunity for knowledge. He believes he can use this new affliction of his to expand his mind and regain the knowledge he lost.
