The Red Wizards of Thay are a fictional organization and social class of evil aligned wizards in the Forgotten Realms campaign setting of Dungeons & Dragons and Advanced Dungeons & Dragons. The Red Wizard prestige class is associated with this organization.
According to the Forgotten Realms Campaign Setting book, Red Wizards are the usually notorious and nefarious spellcasters who are the ruling class in the inhospitable but well-inhabited country of Thay. The Red Wizards are slavers, demonologists, magical experimenters and scholars. They constantly scheme to bring down their neighbouring nations of Rashemen—where they are thwarted by the Witches of Rashemen; Aglarond—where they are turned back by the Simbul of the Seven Sisters; and Mulhorand—where the people of Thay originated. There are certain academies, such as the Academy of Shapers and Binders in Thaymount, that are considered "anomalies" among the Red Wizards, as they discourage betrayal, deceit and slavery; their members show compassion and mercy unlike most others of their kind.
The leaders of the Red Wizards are the eight zulkirs, each for a different school of magic. Chief amongst these is Szass Tam, an undead archmage.
The Red Wizards are described as the enemies of many forces in Abeir-Toril—whilst they receive support from demons and devils and drow, amongst those who oppose them are the Witches of Rashemen, the Seven Sisters and their allies, the goodly Harpers, and even the Zhentarim, who dislike the wizards encroaching on their territory.
The Red Wizards' latest plot, after another failed attempt at securing Rashemen in 1357 DR, is to infiltrate the nations of Faerûn legitimately—in Thayan enclaves which will publicly sell magic items and quietly also traffic drugs, wicked spells, and slaves. Using these they hope to eventually have strongholds and resulting political infiltration that will make them indispensable and powerful, and further their hopes of world domination.
More information about the Red Wizards can be found in the Forgotten Realms Campaign Setting book, and the supplemental Forgotten Realms sourcebooks Lords of Darkness and Unapproachable East.