Hesperdan

Gelvar Thordrunn was a dealer of magical curios and esoterica in Ordulin, Sembia. He took on Malathar Wingstarl (later known as Sememmon) as an apprentice, teaching him wizardry. Gelvar disappeared, believed lost at sea, two years after taking on Malathar, some time between 1234 DR and 1258 DR.

"Gelvar" was actually the mage Hesperdan who did much behind the scenes to foster Semmemmon's rise in the Zhentarim ranks and indirectly sought to mould him to be a foil for Manshoon.