Blizzard Entertainment shared with Blizzplanet and other fansites an image teaser announcing "The Thunder King is risen."
A new raid dungeon featuring The Thunder King will be opened on January 2013 with Patch 5.2 which adds access to The Thunder Isle.
The isle is currently inaccessible in live realms. It's the big isle north of Townlong Steppes in the Pandaria continent.
The storyline about the resurrection of the Thunder King, a powerful mogu emperor, is experienced by players during the quests at the Zouchin Village in Kun-Lai Summit.
The Zandalari trolls resurrect The Thunder King to bring about a new age of fear and terror upon the world of Azeroth.