Jarulf, real name Pedro Faria, is best known as the author of Jarulf's Guide to Diablo and Hellfire. He was one of the first gamers to delve into the game code and share the information (and bugs) he discovered with the Diablo community. Jarulf continued his code delving in Diablo II, though he was not as active a participant in that game's community.
Jarulf was rewarded for his celebrity by having one of the Act 3 mercenaries named after him in Diablo II.