Khelben "Blackstaff" Arunsun is one of the most powerful wizards in Faerûn, a Chosen of Mystra, ex-member of the Harpers and a Masked Lord of Waterdeep.
Baldur's Gate Edit
In Baldur's Gate, Khelben Blackstaff is mentioned by Theodon in Candlekeep, in Chapter Five.
Shadows of Amn Edit
Khelben appears in the City of Caverns as an illusion, created by two imps for their riddle game.