In Erudin Palace: Enchanter Guildmaster.
In Erudin Burning: Located at about -340, 310 (in the area south of the dock area along with several other quest NPCs).
In Erudin Burning (group): Part of the task "The Illuminating Truth" (see this quest entry for task information).
In Erudin Burning (raid): Part of "The Torches of Truth" raid (see this quest entry for event information and loot).