Mordenkainen is a fictional wizard from the World of Greyhawk campaign setting for the Dungeons & Dragons roleplaying game.

[5] Gygax was interested in Finnish mythology, and named the wizard Mordenkainen, a portmanteau of the mythical heroes Mordecai and Lemminkäinen.

[6][3] Kuntz started a role-playing campaign in his Kalibruhn setting in 1973, in which Mordenkainen and Yrag developed as player characters of Gary Gygax.

[8] Over several years of gameplay, mainly from 1973 to 1985, Gygax developed the character traits and adventures with which Mordenkainen would become associated, as well as raising the wizard to "twenty-something levels".

Mordenkainen also figured prominently in the parody adventure Castle Greyhawk (1988), in which he runs a film studio, possibly a reference to Gary Gygax's work at the time as TSR's liaison to Hollywood while he was developing the Dungeons & Dragons cartoon and other projects.

[19] Mordenkainen is described as tall, with a greyly streaked Van Dyke beard, wearing long boots and carrying a staff.

[2] Backstab magazine contributor Kaneda considered Mordenkainen one of the greatest magicians from the Greyhawk campaign setting.