Elminster Aumar is a legendary wizard, originally from Shadowdale. A key bearing his symbol appeared on Diath's key ring while the group sailed from Port Nyanzaru to Waterdeep.  A talking fish delivered a message from Elminster to Strix while the heroes sailed from Port Nyanzaru to Waterdeep. It warned her to keep an eye out for clues from Elminster (part of the Immortal Fortress storyline). 
Elminster Aumar is a legendary D&D NPC who has starred in many novels written by Ed Greenwood. Elminster has appeared in many RPG products, as well as a series of Dragon Magazine short stories in which he spends time with wizards from other settings, including Mordenkainen. Recently, Elminster was featured in Volo's Guide to Monsters as a "co-author" of the in-game version of the tome.