Mekrath

Mekrath was a powerful wizard who lived in his lair below the Athkatla Temple district. He was no very tolerant with visitors, and especially thieves like Haer'Dalis, who he kept as a slave after Haer'Dalis stole his Portal Gem.

In Baldur's Gate II, you will find him in his domain in the Athkatla Sewers. If you came to his lair because of Raelis Shai, you will have to either kill the mage or perform a task for him to retrieve Haer'Dalis.